Heat affect on engine/fuel

[dirtdobber]

Ok guys, I'm looking for an answer to a question, but first the background:

In my Hustler 950, I just did an engine swap. I removed a 20 horse opposed Briggs and replaced it with a 18 horse opposed Briggs. I used the cowling and the carburetor from the 20 horse, and the same exhaust set up. The only substantive difference between the two engines is 2 horsepower, and the 18 horse has the pulley on the flywheel for rope start, if needed. The 20 horse ran fine with no heat related issues.

I took it out yesterday and rode about 10 miles, most of which was hard ground. At the beginning of the ride it ran fine. After a while, it would not idle and was hard to start. I would have to hold the throttle wide open with no choke for it to start, and it wouldn't run under about 1500 rpms. This morning, it ran fine. I assume the fuel was boiling and keeping it from running right.

The real question is why? It's the same engine as was there before with no issues. The only thing I can think of is the flywheel may be different in its ability to move air.

What do you guys think?

[beagle man]

Hey dirtdobber it almost sounds like the float is sticking and its flooding or even the fuel vent is restricted. I know a lot of small engines behave the same way. Also is it possible that you may need to lean out your jets. I realize you have likely looked at these things, just trying to help with the problem.

[ARGOJIM]

Does sound like a flooding issue, the only other thing that comes to mind is maybe the emulsion tube has gotten something in it.
It sounds like a low rpm circuit thing.

[dirtdobber]

I'm going to look at it today. Hopefully I'll have something to report this evening.

[trevorakm1]

first off I'm not an engine guy. I had a B&S 18 horse in my argo bigfoot when I got it used. It didn't take long before I had to have the choke on for it to run and I knew this is not the proper way for it to run. cleaned the hell out of the carb and fixed the need for choke issue. Carb was gummed up jets included. Once clean she purred but found I had to keep playing with the idle screw to get a good idle at different times such as cold start, warm start and hot starts. Also affected by the weather, much worse during warm weather. Drove me nuts. Watching videos and talking to members here who run down south I learned they would remove the hood and ride like that. Again I didn't like that idea either, this should run smoothly and as she was designed. I figures it was all heat issues and that the carb wasn't getting the same temp air through the course of my riding. The inside of engine compartment would get hot and some of that hot air was drawn into carb thus requiring and idle adjustment, let the idle chase begin. So I swapped motors for two reasons, 1 I wanted more power so I got a 23 hp B&S. 2 I also wanted a brand new engine so I knew the history of the motor.
Swap went fine but now more engine heat and now less open space around the motor contributing to the heat issue. Well it occured to me that most of the heat is caused by the muffler and a completely passive means to exhaust this engine heat. So I got two of those computer fans and made a quick rectangular frame for them out of aluminum stock from Lowes. I then mounted this at the inside opening of the exhaust port on the left side of the machine. the tail pipe fits between the two fans and they draw the warm air from around the muffler and tail pipe. Voila heat and idle issue gone. I then changed the brake fan switch to a multi position. So engine starts and I turn the fan switch to the first position and that starts these exhaust fans and when ready to ride I move the same switch to the next position which than adds the brake fan motor, this helps control the electrical draw on the battery while sitting idle. Now she purrs and idle is not an issue anymore.
This may have nothing to do with what you are dealing with but gives some insight on how the heat inside the engine compartment really does affect air density going into the carb.

[dirtdobber]

I fired it up yesterday and it didn't run worth a flip at low rpm. A little adjustment to the mixture screw and idle screw and it runs like a top. Drove it around for a short while and it ran fine. The real test will be the next outing - to see if the head has an effect on it. Trevorakm1 those are good points you raise.

[john swenson]

i know my 21 horse briggs vanguard in my max 2 will run hot after awhile at busco. then it starts missing , etc. i installed a large exhaust fan and it stopped because it's drawing the hot air out which was causing vapor lock. a couple of the guys said move the fuel pump off the motor and way up towards the tank...away from the hot engine . so i'll try that before the next ride . johnboy va.

[oztrax]

Interesting, think I may of had same issue
After 15 mins seems to starve of fuel and stop.
Only needs a couple of mins to recover.

Got better when I also fitted a heat shield 16 gauge stainless
On top of exhaust,then it went for 40 mins or so.
3D8558D9-7A16-4A77-A08F-7207E44485F2.jpg

My problem also self induced, relocating radiator lower down in my Max 4

OZ

[Noel Woods]

Check your fuel pump as well. One of the first Argos I had the heat and starvation issue was perplexing. Eventually I pulled the fuel pump off and noted the backside had melted. I then used some washers to make a stand off mount that gave it another 1/4" or so. That helped alot, and I eventually placed it out a full 1" which worked even better.

[msafi65]

Are you running pure gas or ethanol? The alcohol boils at very low temp.