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C301 problems


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So I have a c301, has the 806 lp high altitude domed pistons in it and the engine was out of a 715 combine with the 715 combine carb on it. The carb has larger fuel line that flows good and fast, the carb is perfectly clean top to bottom and looked at also by a long time ih mechanic. It has the #35 venturi in it and a really high quality manifold gasket. But for some reason it only likes to run choked, it will Rev way high but if you take of choke it will just stop running or spit and shudder. What are your thoughts? Also seems like it should have more power for having an 806 high compression engine in it1617228308815398522596166530877.thumb.jpg.5685c2e498ca8a7ece9819ab0481ae55.jpg16172283230554456027750184573159.thumb.jpg.01654394c02ca959ceaa0e123dfd696f.jpg16172283422856093669734539636983.thumb.jpg.52a05d8ad2d392809ba3e54cb74e35af.jpg

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borrow swap carb for confirmation...

does it have the heat..? riser... broken malfunctioning....vacuum leak....propane test

ours had to be just so and then fully warmed before running correctly

confirm float is flowing enough of this china gas......use ac plugs

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First I would make certain your ignition is in tip top shape, electronics with 12v coil.  I would be running plug adapters and a NGK plug based on a recommendation from the tech line based on the compression ratio, your at what ~8.5:1 a full point over stock?

Then if you are sure you have no vacuum leaks and float is set right.  Timing is set, valves are set.  I would carefully ream out the main jet. 005 at a time.  You can probably go more because you have a tapered metering jet adjustment.

All this is much easier with assistance of a dyno as you can light and heavy load the motor.

Honestly unless your **** bent on max hp a smaller venturi will run better in most conditions.  This why on my 291 build I stuck to my 656 carb...it will atimize better but kill a bit of top end hp but who cares when your on the governor most times.

Remember your higher compression is going to demand more fuel, also if your running 87 octane the ethanol will require 5-10% more fuel as well.  This all could be attributing to your lean stumble or lack of signal accros the venturi.

Also in the past we did business with Denny back in the mid 90's not buying or selling...I seem to remember atleast for pulling the venturi was modified so yours maybe losing signal as it is modified for pulling?

Good luck!

Scott

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10 hours ago, J-Mech said:

In the pic, a bolt is loose.  I'm sure you noticed.

You didn't say, and I'm going to ask.... you did try backing out the main valve right? 

Bolts was loos cause I took it apart to compare venturis, and the valve was tried at all different settings with no change. 

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9 hours ago, mmi said:

borrow swap carb for confirmation...

does it have the heat..? riser... broken malfunctioning....vacuum leak....propane test

ours had to be just so and then fully warmed before running correctly

confirm float is flowing enough of this china gas......use ac plugs

Search for leaks with propane, nothing. The part on the manifold where the heat spring is has the hole welded shut so I don't know what's up with that. I could take that apart and if it's blocked I could just remove the blocked part for now and try

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8 hours ago, 460 said:

First I would make certain your ignition is in tip top shape, electronics with 12v coil.  I would be running plug adapters and a NGK plug based on a recommendation from the tech line based on the compression ratio, your at what ~8.5:1 a full point over stock?

Then if you are sure you have no vacuum leaks and float is set right.  Timing is set, valves are set.  I would carefully ream out the main jet. 005 at a time.  You can probably go more because you have a tapered metering jet adjustment.

All this is much easier with assistance of a dyno as you can light and heavy load the motor.

Honestly unless your **** bent on max hp a smaller venturi will run better in most conditions.  This why on my 291 build I stuck to my 656 carb...it will atimize better but kill a bit of top end hp but who cares when your on the governor most times.

Remember your higher compression is going to demand more fuel, also if your running 87 octane the ethanol will require 5-10% more fuel as well.  This all could be attributing to your lean stumble or lack of signal accros the venturi.

Also in the past we did business with Denny back in the mid 90's not buying or selling...I seem to remember atleast for pulling the venturi was modified so yours maybe losing signal as it is modified for pulling?

Good luck!

Scott

I have 93 non oxygenated gas in it. It has the igniter electronic ignition with msd coil and the factory recommended plugs. And I compare the venturi that was in it to a stock #35 and they looked identical. I would like to be able to run it with the right venturi since I'm pulling with it, its an 806 engine and it would be nice fore it to have 806 power

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9 hours ago, mmi said:

borrow swap carb for confirmation...

does it have the heat..? riser... broken malfunctioning....vacuum leak....propane test

ours had to be just so and then fully warmed before running correctly

confirm float is flowing enough of this china gas......use ac plugs

Also I was wondering, why is it some people want lp manifolds for hp where the intake and exhaust are separate so it runs cooler but then others need a heat exchange? Never understood that

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36 minutes ago, Rusty shackleford said:

Also I was wondering, why is it some people want lp manifolds for hp where the intake and exhaust are separate so it runs cooler but then others need a heat exchange? Never understood that

Application.  Depends on build and application.

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44 minutes ago, Rusty shackleford said:

Bolts was loos cause I took it apart to compare venturis, and the valve was tried at all different settings with no change. 

No change?  At all? If you screw it all the way in does it die?

Sounds like you have a blockage, or incorrect fuel level in the bowl. 

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2 minutes ago, J-Mech said:

Application.  Depends on build and application.

This would be mostly tractor pulling, and some some time yard use. Mostly want it to run like a strong factory engine

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1 minute ago, J-Mech said:

No change?  At all? If you screw it all the way in does it die?

Sounds like you have a blockage, or incorrect fuel level in the bowl. 

It does die when you screw it all the way in, and once it's started to screw out it dosnt effect whether you need to choke it or not .

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1 minute ago, Rusty shackleford said:

It does die when you screw it all the way in, and once it's started to screw out it dosnt effect whether you need to choke it or not .

Yep.  Blockage, wrong main jet (that the needle goes against) or low fuel level in the bowl.  

Did this happen suddenly? 

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1 minute ago, J-Mech said:

Yep.  Blockage, wrong main jet (that the needle goes against) or low fuel level in the bowl.  

Did this happen suddenly? 

It will run almost perfect as long as you have the choke set at the right amount, will Rev all the way up and never studder as long as the choke is pulled like 3/4 out. Everything on the carb is set up for moving more fuel and the fuel line is extra big and poors very fast. I had a guy who has been an ih mechanic his whole life look at it and even he scratched his head on it and tried a bunch. He got it going way better than it was but it still needs to be choked.

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5 minutes ago, Rusty shackleford said:

It will run almost perfect as long as you have the choke set at the right amount, will Rev all the way up and never studder as long as the choke is pulled like 3/4 out. Everything on the carb is set up for moving more fuel and the fuel line is extra big and poors very fast. I had a guy who has been an ih mechanic his whole life look at it and even he scratched his head on it and tried a bunch. He got it going way better than it was but it still needs to be choked.

Choke on means it is running lean, not getting enough fuel.  Problem has to be in the carb, or a vacuum leak, but you tested for that and found none. Keep looking.  Problem is in the carb.

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My guess is the main jet is too small.  Can turn the main screw out all you want and not get enough fuel if that is the case.  If this engine is high compression you definitely don’t want to be on the lean side if you are going to pull it hard.  If you have access to more main jets, you could just take one and drill it out with an appropriate size drill bit to verify if this is the problem.  A little enlarging goes a long ways.  

Since this IS a Denny’s carb, I would verify that it has the correct jets in it in the first place . . . 

Having to use the choke to correct the mixture is killing your power also . . . air restriction.

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we have 3 706 tractors with c-301 combine motors. they all run fine on 87 octane pump gas and have the combine carburetors.

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Another thing to check is ignition timing. I very much doubt it would be the only problem but if it is too advanced it would aggravate the tendency to stumble and cut out if the fuel mixture is already lean. 

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2 hours ago, J-Mech said:

Choke on means it is running lean, not getting enough fuel.  Problem has to be in the carb, or a vacuum leak, but you tested for that and found none. Keep looking.  Problem is in the carb.

16172945425742483900919664775750.thumb.jpg.175bca028f49de47c3f305eb102e12ac.jpg16172945727304692659595938456750.thumb.jpg.20893e789d951bac648bfbefc8e8ece6.jpgprobably can tell from pics but you can see on the top pic where it's rubbing for it bottomed out, and the the size of the hole on the next pic. 

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1 hour ago, Rusty shackleford said:

16172945425742483900919664775750.thumb.jpg.175bca028f49de47c3f305eb102e12ac.jpg16172945727304692659595938456750.thumb.jpg.20893e789d951bac648bfbefc8e8ece6.jpgprobably can tell from pics but you can see on the top pic where it's rubbing for it bottomed out, and the the size of the hole on the next pic. 

Jet looks too small. 

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3 hours ago, randy hall said:

we have 3 706 tractors with c-301 combine motors. they all run fine on 87 octane pump gas and have the combine carburetors.

 

2 hours ago, snoshoe said:

Then you have three examples to verify jet size but if they are standard compression you may still have to go larger.

Crap. Thought it was Rusty's post. Must be the dementia the're talking about in the cab thread.

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SUCCESS , I drilled out the main needle valve just a tiny bit and reemed the jet out just a Nats butt hair and that did it, revs up all the way now without a choke. Now I can tune from there. That derptard dennys carb shop must have put m parts in there. Thanks for all the help everyone now it's deere hunting time

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