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New around here, SV735 fast idle surging issue. Already tried all the obvious things

#1

T

TT_Vert

Hey guys, this is my last ditch effort at figuring this issue out. My Cub Cadet w/ a Kohler SV735 idles at slow speed fine but on high speed it surges. I can definitely see the governor moving back and forth causing the surging which I've read is generally a lean condition on these.

I've done the following:
1. Adjusted the governor to ensure the shaft is up against it at the correct linkage position,
2. Disassembled the carb, removed the main jet and ran small bristle brushes through all passages, ran carb cleaner through them all and also compressed air. The carb looked brand new inside.
3. Removed float and ensued needle sealed properly. Float level seems fine but i"m basing it off of auto carb float levels.
4. I've not yet checked for vacuum leaks at the intake and carb base but I'd assume if there was a leak it'd rear its head at low speed idle as well.
5. Removed filter to ensure it wasn't restricting flow even though it's fairly new.
6. Removed gas gap to make sure there was no issue w/ fuel flow or vacuum cavitation.
7. Ensured fuel filter was flowing well.

Thanks for any input you can offer.

Dave


#2

I

ILENGINE

Sounds like a partial blockage of the idle circuit in the carb. You are getting enough full to idle fine but at higher rpm's you are not getting enough at no load full throttle through the idle circuit.


#3

T

TT_Vert

ILENGINE said:
Sounds like a partial blockage of the idle circuit in the carb. You are getting enough full to idle fine but at higher rpm's you are not getting enough at no load full throttle through the idle circuit.
Click to expand...
After taking this carb apart and seeing how clean it is cannot see how anything is blocked. I also didn't pass carb cleaner and compressed air through each orifice. How can I get to the idle circuit? There's only one jet in this thing which is clear and there are a couple other things that are plugged.

Also now I've noticed that is not slow idling properly unless I have the choke partially closed just like with fast idle to get our to stop surging.

Dave


#4

B

bertsmobile1

Air , like any other fluid takes the path of least resistance.
An air leak through a bad manifold gasket is DRIVEN by the venturi effect of the air rushing into the engine.
Thus at low revs there is little pressure to suck air through the difficult high resistance path via a leaking gasket or manifold.

The first rule in mechanical diagnosis is nothing gets RULED OUT .
Potential problem points are TESTED OUT

Start the engine then put your finger on the governor arm and hold it steady.
Slowly push it forward to increase the speed.
If you can hear the engine sputtering and missing then you are not getting enough fuel and if the starvation is big enough, it will cause the engine to shut down all together.

Every hole in a carburettor will lead some where so every hole has to have cleaner sprayed through it and the outlet checked
I like to blow backwards through them from the engine side so you blow debris out.
There are two circuits in the carb and both have their own air passage & fuel passage then on top of this there is an air inlet into the float bowl.
All of them have to be clean.
Go to http://outdoorpowerinfo.com/repairs/ and follow their cleaning proceedures.


#5

T

TT_Vert

bertsmobile1 said:
Air , like any other fluid takes the path of least resistance.
An air leak through a bad manifold gasket is DRIVEN by the venturi effect of the air rushing into the engine.
Thus at low revs there is little pressure to suck air through the difficult high resistance path via a leaking gasket or manifold.

The first rule in mechanical diagnosis is nothing gets RULED OUT .
Potential problem points are TESTED OUT

Start the engine then put your finger on the governor arm and hold it steady.
Slowly push it forward to increase the speed.
If you can hear the engine sputtering and missing then you are not getting enough fuel and if the starvation is big enough, it will cause the engine to shut down all together.

Every hole in a carburettor will lead some where so every hole has to have cleaner sprayed through it and the outlet checked
I like to blow backwards through them from the engine side so you blow debris out.
There are two circuits in the carb and both have their own air passage & fuel passage then on top of this there is an air inlet into the float bowl.
All of them have to be clean.
Go to http://outdoorpowerinfo.com/repairs/ and follow their cleaning proceedures.
Click to expand...
I did check for vacuum leaks but was unable to edit my original post to reflect this. I introduced propane around both intake to head gaskets as well as the base of the carb w/o any change in performance so I think I can safely rule out any sort of vacuum leak. I can rev the engine smoothly so it appears AFR is close. I did blow out each passage (With carb cleaner and air) that was not caped w/ a plug. I don't have an exploded diagram of the carb to get any more idea of what these plugged passages do. I know the main jet that comes up from the bowl exists and that is it. The entire carb looked new before I did a thing to it. The tractor is only a few years old and I drain the fuel out before each winter. Up until last year it was always stored in a heated garage.

But again I have updated that after reassembly it will have a tendency to want to die at slow speed idle unless I have the choke closed some. SO now, slow speed idle is very low and wants to die unless I slightly choke it and high speed surges unless I slightly choke it. Makes me think it's actually rich.

Dave


#6

I

ILENGINE

If it smooths out with partial choke then you have a carb problem. Adding choke proves the engine is running lean not rich. Lean on the idle circuit causes a surge because the engine without enough fuel on the idle side will start the slow and as it slows it tries to open the throttle which in turn then opens the high speed jet and the engine speed picks back up, and then starts to slow back down and is running lean on the idle circuit and the cycle repeats.


#7

B

bertsmobile1

And propane gas around the manifold is dangerous , stupid and ineffectual
Dangerous :- the gas can ignite
Stupid :- because of the above & potential for serious injury
Ineffectual:- because of the dilution effect
Saturating the manifold with WD 40 is the very best way to do it from a trigger pack, not a spray can because the propellants are also volatile.
WD 40 will not damage the engine but will create a lot of dense white smoke so even if you do not hear a change in engine speed you will see the smoke.


#8

T

TT_Vert

bertsmobile1 said:
And propane gas around the manifold is dangerous , stupid and ineffectual
Dangerous :- the gas can ignite
Stupid :- because of the above & potential for serious injury
Ineffectual:- because of the dilution effect
Saturating the manifold with WD 40 is the very best way to do it from a trigger pack, not a spray can because the propellants are also volatile.
WD 40 will not damage the engine but will create a lot of dense white smoke so even if you do not hear a change in engine speed you will see the smoke.
Click to expand...
I think you're being a bit dramatic here. IN 30+ years I've never seen anyone have any issue w/ using propane to find a vacuum leak in any IC engine. People also use oxy/acetylene torches and still have all of their limbs. You do not ignite the propane externally. many people swear by propane as it works and is cheap/easy to obtain. Heck, even popular mechanics suggests doing it and I doubt they would in this litigious society if there even a hint of danger in doing it. I do agree with you in this situation is the fan blows the propane around diluting it to the point of not being very effective and you'll see the byproduct of burning WD40. I'm generally not a fan of spraying liquids in my engine bay to find leaks so I generally don't do it.




ILENGINE said:
If it smooths out with partial choke then you have a carb problem. Adding choke proves the engine is running lean not rich. Lean on the idle circuit causes a surge because the engine without enough fuel on the idle side will start the slow and as it slows it tries to open the throttle which in turn then opens the high speed jet and the engine speed picks back up, and then starts to slow back down and is running lean on the idle circuit and the cycle repeats.
Click to expand...


Thanks, I was bass ackwards on this for some reason, brain fart. I'm not sure how to proceed w/ this as I'm certain every passage on this guy is clear. I've also confirmed good fuel into the pump and the float is not adjustable as the needle slides into a channel on the plastic float..


#9

B

bertsmobile1

Using propane seems to be a USA specific idea and while you are right, the chances of a Whoof is low that still does not make it a good idea.
IT also does not work particularly well in any situation other than on a V8 where you have a dam for the gas/air mixture to accumulate and strong induction.
Nothing wrong with putting a liquid on a mower engine, or any engine for that matter just so long as you avoid the electronics & exhaust.
Motorcycle engine happily run in the rain & there is not too much difference between a mower & a motorcycle.
if you are a wash after use type person then you would be doing it regularly.
You sound like you know your way around engines so the fact that being slightly choked makes the problem go away should say too lean in the back of your brain.
EPA requirements have mower engines running way too lean for their own good to start with so it take almost nothing in the way of obstructions to cause them to surge .
Go to the site I linked to and see if you can find your carb.
They have gone to the effort of cutting a lot of them up so you can see where the various passages go.

On the very left field side, if the shut down plunger has a rubber cap on it these can come loose & partially block off the feed to the fuel jets.
Usually it becomes a problem at WFO where the venturi effect sucks the rubber cap into the opening.

It would also help if you mention which carb you have on the engine.

And for your benefit, Kohler have all of their repair manuals on line as a free download so it would be worthwhile getting your hands on one.
We are all here to either help you or get help.
It is not face book when 2/3 of the posters are there trying to inflate their position by tearing others down.


#10

T

TT_Vert

bertsmobile1 said:
Using propane seems to be a USA specific idea and while you are right, the chances of a Whoof is low that still does not make it a good idea.
IT also does not work particularly well in any situation other than on a V8 where you have a dam for the gas/air mixture to accumulate and strong induction.
Nothing wrong with putting a liquid on a mower engine, or any engine for that matter just so long as you avoid the electronics & exhaust.
Motorcycle engine happily run in the rain & there is not too much difference between a mower & a motorcycle.
if you are a wash after use type person then you would be doing it regularly.
You sound like you know your way around engines so the fact that being slightly choked makes the problem go away should say too lean in the back of your brain.
EPA requirements have mower engines running way too lean for their own good to start with so it take almost nothing in the way of obstructions to cause them to surge .
Go to the site I linked to and see if you can find your carb.
They have gone to the effort of cutting a lot of them up so you can see where the various passages go.

On the very left field side, if the shut down plunger has a rubber cap on it these can come loose & partially block off the feed to the fuel jets.
Usually it becomes a problem at WFO where the venturi effect sucks the rubber cap into the opening.

It would also help if you mention which carb you have on the engine.

And for your benefit, Kohler have all of their repair manuals on line as a free download so it would be worthwhile getting your hands on one.
We are all here to either help you or get help.
It is not face book when 2/3 of the posters are there trying to inflate their position by tearing others down.
Click to expand...

I appreciate the help for sure.

Agreed, most modern connectors are moisture resistant and not an issue. I'm more opposed to it on my cars as I don't want to have to clean any residue off my engines or risk having it discolor aluminum or composite materials as it burns into them. I'd mention what carb I have if I knew exactly LOL. I'll have to take off the airbox again to take a look. I see no PN stamped into it and the service manual I found for my engine shows a different image of the carb. They are similar but mine does not have the flat top piece secured w/ fasteners (See attached pic). KH-32-853-28-S is the PN for the Kohler SV735 according to what I've located. Every place I google SV735 carb I find this one I'm showing.

Tomorrow I may pull the shutoff solenoid again (had no cap, just a needle that closed off the jet) and see if it is in fact not retracting enough as that makes a bit of sense. It seemed to be free when I tore it down but I don't know if I'm hearing the solenoid engage when i'm keyon but I don't know that I paid any attention to that to be honest.

BTW, none of those kohler carbs are exactly what I have but the closest is the walbro LMK carb. It mentions a low idle fuel adjusting needle but unless it's under one of the welch plugs I don't have this either. Would you mind telling me when you find the kohler manuals? I've not found any manual for the 3285325-S. I found thisbut my Kohler carb isn't in there.

SV735.jpg
Dave


#11

B

bertsmobile1

TT_Vert said:
I appreciate the help for sure.

Agreed, most modern connectors are moisture resistant and not an issue. I'm more opposed to it on my cars as I don't want to have to clean any residue off my engines or risk having it discolor aluminum or composite materials as it burns into them. I'd mention what carb I have if I knew exactly LOL. I'll have to take off the airbox again to take a look. I see no PN stamped into it and the service manual I found for my engine shows a different image of the carb. They are similar but mine does not have the flat top piece secured w/ fasteners (See attached pic). KH-32-853-28-S is the PN for the Kohler SV735 according to what I've located. Every place I google SV735 carb I find this one I'm showing.

Tomorrow I may pull the shutoff solenoid again (had no cap, just a needle that closed off the jet) and see if it is in fact not retracting enough as that makes a bit of sense. It seemed to be free when I tore it down but I don't know if I'm hearing the solenoid engage when i'm keyon but I don't know that I paid any attention to that to be honest.

BTW, none of those kohler carbs are exactly what I have but the closest is the walbro LMK carb. It mentions a low idle fuel adjusting needle but unless it's under one of the welch plugs I don't have this either. Would you mind telling me when you find the kohler manuals? I've not found any manual for the 3285325-S. I found thisbut my Kohler carb isn't in there.

View attachment 45894
Dave
Click to expand...

Kohler used Nikki & Keihin carbs \The latest manual number I have is # 32 690 01 Rev. D
Go to the Kohler USA web page then under customer support go to manuals
If you come to a log in page log in as "guest"
Then type in you model & serial numbers and it should bring up the operators, parts & service manual
32 690 01 Rev. D covers the engines SV 710 to 740 & SV 810 to 840


#12

T

TT_Vert

bertsmobile1 said:
Kohler used Nikki & Keihin carbs \The latest manual number I have is # 32 690 01 Rev. D
Go to the Kohler USA web page then under customer support go to manuals
If you come to a log in page log in as "guest"
Then type in you model & serial numbers and it should bring up the operators, parts & service manual
32 690 01 Rev. D covers the engines SV 710 to 740 & SV 810 to 840
Click to expand...
Thanks,
I actually just got 32 690 01 Rev. H from there( i assume that is newer than Rev. D) and it shows 3 carb options (Nikki, Keihin and Walbro). Based on the exploded diags none of those are what I have on this thing. They all have an idle fuel adjusting screw near the base of the carb at the top which mine does not have.

Dave


#13

B

bertsmobile1

Dave,
Well you are at the limit of my knowledge on this one.
The idle adjustment is not a fuel jet
If it is in the flange then it is a passage way metering jet that controls the volume of the idle air / fuel mixture that enters the carb throat.
Some have a removable idle jet that is usually under the plastic throttle stop , these pull out after the screw is removed then you blow then whole thing out from there.
A photo of your carb will help .
I am an independent workshop so tend to see mowers that are quite old or where the dealers tell the customer "can not be repaired but we will give you a good deal on,,,,, "


#14

I

ILENGINE

You are thinking if terms of clean meaning there is no debris in the passages, but in this case could be a piece of aluminum corrosion that is part of the carb and will not be blown or sprayed out.


#15

T

TT_Vert

ILENGINE said:
You are thinking if terms of clean meaning there is no debris in the passages, but in this case could be a piece of aluminum corrosion that is part of the carb and will not be blown or sprayed out.
Click to expand...

Thanks guys. I did blow out each passage both ways w/ air and liquid and given how clean this carb is (Looks new inside) I'd be hard pressed to think any aluminum debris or corrosion would be in there, or any for that matter. It's probably the cleanest carb I've torn down. Either way,I'm going to yank the carb again in a bit and get some pics and go through each passage again. I'm also going to test the fuel pump and that fuel shutoff solenoid a bit more as that could also cause my lean condition. These carbs are so simple i'm surprised I've not figured this one out yet. For comparisons sake the first carb I ever tore down was a quadrajet out of a 82 chevy van. In fact that's the first carb I ever rebuilt, with only the aid of the rebuild kit info which was very sparse. If i could figure that out I certainly shouldn't be defeated be a fricking 1BBL lawn tractor carb.

Dave


#16

I

ILENGINE

Dave you are thinking in too big of components. This could be a 4 micron obstruction in a 8 micron passage that is cross drilled and then sealed off at the factory.


#17

T

TT_Vert

ILENGINE said:
Dave you are thinking in too big of components. This could be a 4 micron obstruction in a 8 micron passage that is cross drilled and then sealed off at the factory.
Click to expand...
fair enough, not sure how I could rectify that then. Have the carb off and there is a plug Where most have an adjustable idle air screw sadly. I don't have spare plugs to knock this thing out but adjusting that would be a bandaid anyway as something is awry somewhere here. Will update in a bit.




Dave


#18

T

TT_Vert

TT_Vert said:
fair enough, not sure how I could rectify that then. Have the carb off and there is a plug Where most have an adjustable idle air screw sadly. I don't have spare plugs to knock this thing out but adjusting that would be a bandaid anyway as something is awry somewhere here. Will update in a bit.




Dave
Click to expand...
Took it all apart again and used a stainless wire bristle to ensure the idle passages were not blocked and they were not. Then ran electronics cleaner (All I had handy) through each passage and saw it coming out perfectly fine. Same from every other passage. Also confirmed fuel pump and the fuel cutoff solenoid are perfectly functional. I did adjust the linkage a bit and the idle speed screw a tad and it's doing better but I still have that same fast idle surge I've always had. I actually have another carb coming to test and at this point I'm going to have to look hard and fast at these intake gaskets I think. PN of this carb is 3205328 and it's made by Kohler.



Dave

Attachments















#19

T

TT_Vert

sorry for the multiple posts, i'd edit if I could. I put on a cheap $40 amazon carb from presumably china and the problem went away after I did some tuning on it for other issue (Idle, AFR, etc.). Starts and runs perfect now. Idles steady at 1225 RPMs slow and 2950 fast, no more surging. I have ZERO idea where the issue is on this carb but there has to be some passage I cannot get to that is partially blocked. Every passage flows air/fluid just fine so I really am at a loss. Perhaps there is some bypass passage internal that I cannot see that is clogged. The original car ran fine, started well and never surged under load. It just drove me crazy listening to that surge while it was stationary at high idle. I suppose I could have just gone to low idle but that's just not me. I'd rather spend 2 days troubleshooting an issue that has zero effect on the function of the machine.

Dave


#20

I

ILENGINE

Dave, don't feel bad, this type of thing happens every day in lawnmower shops across the world, and then customers wonder why we just replace the carb in a lot of cases instead of just cleaning and repairing the old one.


#21

B

bertsmobile1

ILENGINE said:
Dave, don't feel bad, this type of thing happens every day in lawnmower shops across the world, and then customers wonder why we just replace the carb in a lot of cases instead of just cleaning and repairing the old one.
Click to expand...

Also why we either fit genuine parts or parts that come from a certified supplier who will take them back if we find them to be defective.
Sorry itt happened to you in 7 years and over $200,000 ( Aus) in parts the only things that I have had problems with were in line fuel taps that has neoprene seals and Stens replaced the entire trade pack of 50 without question and thanked me for bringing it to their attention.
OTOH I no longer fit Jackmax parts because most of their swing back blades were not deburred properly and when I brought that to their attentione I got "what do you expect for that price ".


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