# Cub Cadet RER - fuel flow problem



## rlah

I'm trying to get my Cub Cadet 804 rear engine rider (vintage 1989?) to work more smoothly. After mowing maybe 10 minutes, the 8 HP Briggs motor starts cutting out, loosing power. After much investigation, I am now *sure* the problem is gasoline boiling. I know this because I can see it thru the clear fuel lines. Every time the engine starts cutting out, I look back and can see the clear line is almost empty. When I shut the engine off and look at it for awhile, I can see the bubbles coming back out of the carb... and blocking the gravity fuel flow from the gas tank. I solved the problem temporarily by mounting the fuel tank at a higher elevation... maybe 4-5" higher and the problem largely goes away. 
This problem seems to be a general one for this model rider... I bought another almost identical mower off <a href=http://www.dpbolvw.net/click-1606754-2202639 target=_blank>eBay</a><img src=http://www.awltovhc.com/image-1606754-2202639 width=1 height=1 border=0> about a month ago - a model 1106 - 11 HP Briggs. After mowing with it about 10-15 minutes, it too started cutting out. I could hardly believe that it had the same problem, so I put a clear fuel line in it and sure enough - gasoline bubbles were coming out of the carb blocking the fuel flow, causing the fuel line to be nearly empty from the filter to the carb. Sorry to be so wordy about this but I suspect many would think the problem would be something else wrong with the carb. But, again, I know the problem is gas boiling. (I long ago tried cleaning the carb.) 
Some pictures of the riders and close-up of the carb area are here:
http://www.pbase.com/rlah/cub_cadet
Has anyone had experience with this type of problem and, more to the point, does anyone have a solution other than my temporary solution of mounting the gas tank in an unhandy higher position? Maybe some type of add-on fuel pump would help? Anti-boiling additive? 

Thx for any help on this thorny one. 
rlah


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## scrench

sounds like the tank isnt venting right ,,, have you tried taking the cap loose ? vapor lock ? well i wouldnt think so but im still learning after looking @ the pictures could be boiling fuel in the bowl i think there should have been a heat shield arround the exaust port looks like someone put a drag pipe on that one , but i would take off the gas cap and see if that fixes it first


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## bugman

also make sure the filter is flowing good in the tank, ( little screen ) and inline filter, it could be the cap......


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## rlah

I've tried many things... cleaned tank, cleaned fuel lines, new fuel filters. You may notice the 2 red filters which are brand new... these haven't worked. I think I have tried running without the gas cap but I can't remember.
Heat shield - the 804 (front mower in picture of both mowers) has the muffler mounted right next to the block. 
I've added more pictures to the gallery above:
http://www.pbase.com/rlah/cub_cadet
You will notice in the third picture (804 - carb, exhaust area) there is a metal shield mounted between the muffler and carb. The designers seemed to know there could be a problem. But it wasn't enough... 10-15 minutes of summer mowing brings bubbles and a stalling engine. You will notice the 1106 has the muffler mounted outside the engine compartment. When I bought it, I had hopes it would run better, but a few days of mowing proved me wrong - evidently even this has enough heat to cause boiling.
If I pull the choke out a bit on either mower, it helps. But I would like to fix the problem.

I will try running without a gas cap just to verify if it helps or not. Any more suggestions or comments? (Thx for responses so far from you experts!)


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## scrench

make sure the throttle shaft is not worn in carburator ,


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## rlah

I've got a solution and it's probably the one I'll stick with - unless someone has a better idea. 
See my picture gallery - the last 2 pictures. I installed a Tee in the fuel line next to the carb and put in a vent pipe to give the boiling gas vapor a shorter way of escape. I just got done mowing for 30 minutes without *any* engine cutoff - much improved! The last picture shows the effect of the hot engine - gas vapor continually streaming out of the carb and bubbles escaping out of my new 'vent' pipe. There are a few bubbles coming in from the gas tank side but most vapor is coming from the carb. This 'vent' pipe has allowed enough gas to enter the carb to keep the engine fed.

This solution is better than mounting the gas tank higher - it was very unhandy sticking out the side of the engine shroud. I'll proceed with installing the same vent pipe on my 804.

scrench: would a worn throttle shaft cause this problem, i.e. if I rebuild the carb, do you think it might help the situation?


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## scrench

well it could cause the engine to run hotter than it should an intake leak worn throttle shaft or improper valve setting will cause an engine to run hot , an air leak will cause a lean condition . which could be causing the heat problem i personally have never seen one boil fuel in the carburator , something is causing it to get that hot , cooling fins could be dirty , low on oil, engine running to many rpm , something binding causing engine to work harder , sounds like it might be an air leak causing heat ,


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## edwardj

This is an interesting problem. I looked at the pics of the two cadets and noticed both were using galvanized pipe for exhaust. Iron pipe does not get rid of the heat as quickly as the thinwall stuff. It retains heat. It would be interesting to take an IR temp reading on the exhaust; you would see a big difference. Any thing you do to make the engine run richer will make it run a little cooler and possibly reduce the the bubbles. If the fuel isn't boiling, the bubbles could be outside air from engine vacuum intended for the fuel pump. When I first read the post I thought "restricted fuel line" but it's centered around a design problem at the exhaust.


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## rlah

scrench:
Thx for the info on carb issues. I have noticed the throttle shaft was a little loose on the 804. I haven't checked this on the 1106. I just rebuilt the 804 to replace a broken connecting rod - I cleaned the cooling fins thoroughly - they were quite dirty. But the 1106 that I bought about a month ago hardly has any dirt in the engine area - although I haven't pulled the flywheel shroud off to look at the cooling fins; plenty of oil in the crankcase. But your idea of an air leak makes me wonder about rebuilding the carb - are carb rebuilding kits good for taking care of worn throttle shaft problems?

edwardj:
Actually only the 1106 model tractor has iron pipe out of the engine. The pipe leads to a muffler outside the body frame - see the second picture of both tractors - the 1106 is closest. The 804 has a factory muffler out of the exhaust port and it has a heat shield - see the third picture "804 - carb, exhaust area". There is no fuel pump on these riders - just gravity feed (and not enough gravity). I might play with your idea of running rich to run cooler.

For those who haven't seen gasoline boiling out of the carburetor into the fuel line, don't miss my picture, the last one of 8 pics! Can't argue with this picture... it's seems to be a one-of-a-kind, make that two-of-a-kind... *both* tractors do this, not just one.


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## scrench

you dont get the throttle shaft in a carb kit its a part all to its own


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## mikemerritt

Very unusual pair of problems. I have never heard of boiling gas in a small engine, not in 30 years. I always heard hot gas wouldn't burn so maybe you have something. Have you pulled the fuel line to feel the temp of the gas? I sure doubt its going to be anywhere near boiling. I wonder what the boiling point of gas is? I wonder if the fuel was truly boiling how the gas lines could take it. 

I think you have a vent problem. Note that gas can't get into the carb bowl area if air can't get out.

Hard to understand it on the new one and WAY to odd that you have two machines with EXACTLY the same symptoms.

Mike


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## rlah

scrench - maybe I'll look for a complete rebuilt carb... (?)

mikemerritt - ...30 years - wow - I suspect there are hundreds of years experience looking at this problem on all the forums I have posted this question. I am truly astounded why someone else has not experienced this problem. I fought it for 5 years - ever since I bought the 804 used about 5 years ago. It would run fine until it heated up and then start cutting out. Only other solution I found to work was mount the gas tank 4"-5" higher for more gravity. Maybe all other rider/tractors have the gas tank mounted higher to the carb and the boiling bubbles can escape back to the tank better.
I liken this problem to 'vapor-lock' on cars. Even though they have fuel pumps, the net result is the same - a starved engine.
Someone else on another forum mentioned the carb venting... I don't know these carbs well enough to know if they are supposed to vent gas vapor from the fuel bowl. If you mean gas tank venting, I've tried running with the gas cap off - no help.
A continued thx to all you experts... I may not be an expert but I can see where the experts are.


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## mikemerritt

Destroyed my first mower in "73 when I was all of 13. We had an old mower and the more I looked at that thing the more I HAD to know what was inside it. Actually it did run again, just not like it did. Started at a mower shop in "75 for some real on the job training, been at it since.

I will ramble around here because you can't seem to do more than one qoute @ H/Talk. 

Have you verified that it is really a lack of fuel when the engine starts stumbling?
This is easily done first by adding choke to see if it helps the way it runs. If not, try spraying starting fluid into the carb throat to see if the engine picks up any. If there is a lack of fuel you can add some by fogging the spray into the carb and actually make it run smoothly as long as you add spray. If you can do either of these and get results you sure have a lack of fuel. The reason I go here is the problems you are having sound just like coils breaking down. I would be very tempted to get a good used coil off of something and try it. 

All bowl carbs have a vent that allows air to get out of the bowl so gas can go in. If the vents blocked you might as well be out of gas. The carbs you have are almost alike and the vent, if I remember right, is identical. Its under the removable baffle on later models and wide open on earlier engines. Its easily cleaned if needed. 

As was mentioned, a faulty gas cap vent can cause everything that is happening here. 

If for some reason there is sluggish gravity flow a vapor pump could easily be added. You would need the pump and another breather with an extra hookup on it for the vacuum line. 

I doubt taking the slop out of the throttle shaft will help this problem though it could help the general running of the engine, particularly at idle.

I think once you fix these engines I would bet my torque wrench that the problem isn't boiling gas. I know you have bubbles but I just can't see hot gas.

Let us know as you go along.

Mike


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## scrench

how deep is the float ? also gas might eat that clear tubing. i dont think the fuel is boiling i have never seen it boil on anything , i would take the kill wire off the coil and run it and see if it cures it first .that will by pass all wiring seat switches ect ,


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## rlah

mikemerrit:
I have indeed verified the fuel starving... I poured a little gas into the air intake and it would run smoothly - at least as long as I dribbled the gas. And as I mentioned somewhere else, a little pull on the choke and it generally runs better, at least much less cutting out. (I think you would loose that torque wrench - I've been studying this problem for 5 years.) Those clear gas lines showed the problem to me - I could clearly see the bubbles as the engine heated up. Then as the engine got hotter, the line went almost entirely empty from the gas vapor pushing out the carb. The last picture in my gallery shows the nearly empty line from the carb to the tee. That is caused by so much gas vapor from the boiling.

Coil breakdown - does this *only* come on when the engine heats up and not before? If so, I may try either your idea of a new coil and/or scrench's idea of disconnecting the kill wire - at least on one of the riders.

Vapor pump - this sounds intersting to me - where can I get one of these? I'm not familiar with this. Is this something at the auto parts store?


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## rlah

mikemerritt:
Wish I knew where that carb vent was that you talked about. I'd like to verify that they aren't blocked. The engines are B&S models 193707 (8HP) and 253707 (11HP).


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## mikemerritt

I think I would have to have my 1/2 inch wrench ready and the next time I thought the gas was boiling I'd drop the bowl nut/screw and determine whether I'd stick my finger in the gas as it runs out of the bowl, IF it runs out of the bowl. I suspect that it would be no problem from a heat point of view. You be the judge of that, you have been at this anomoly a while. 

Coil breakdown.....most common symptom is once an engine reaches a certain temp they cause anything from a slight miss to a no fire situation. As time goes by the symptoms can change for better, worse or not at all. 

Vacuum pumps.....most any rider that has a remote tank, say under the seat etc. will likely use a vacuum pump. You would also have to get a vacuum source for it. B&S has a breather with a hose hookup but they are sort of scarce for these HP engines.

Mike


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## rlah

mikemerritt, scrench, and others:

Those who suggested looking at the carb vent may have the best suggestion for solving this one (I think). This topic was carried out even further on the GardenWeb forum and so I will be attempting to clean the carb(s) again making sure the bowl vent is clear. It seems to me a clogged bowl vent would directly affect the gas boiling (or fuel percolation) problem. Maybe I didn't clean the carb well enough when I tried this several years ago.

I'll try to post results if I get to do this in the next 2-3 weeks. Thx to all for the comments and suggestions.


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## cleancutinc

Noticed The Carb Model Used On Your Engines Have Hrizontal Choke Shaft And Verticle Throttle Shaft,these Carbs Are Very Touchy About Hispeed Mixture (air/fuel) The Bowl Screw On Most Of These Carbs Is A Mixture Screw With A Lock Nut Is This How Yours Is?


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