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vapor lock

m1west

Well-known member
GOLD Site Supporter
I have a thiokol 603, took it to the mountain last week and had a carb. issue once warmed up. At first thought float stuck as gas was coming out of carb. it wasn't until I was putting snow all over it to prevent a fire that I discovered as soon as I did that it ran fine until the next time. I plan to insulate the lines along with a wood spacer under the carb along with electric pump at tank boosting mechanical pump. also thought about a cold air intake from outside the cab as I think the fuel is boiling in the carb. is the problem area. except for AV gas to solve the problem anyone else have any ideas. Thanks Martin
 

Kristi Kt-4

Member
I have a thiokol 603, took it to the mountain last week and had a carb. issue once warmed up. At first thought float stuck as gas was coming out of carb. it wasn't until I was putting snow all over it to prevent a fire that I discovered as soon as I did that it ran fine until the next time. I plan to insulate the lines along with a wood spacer under the carb along with electric pump at tank boosting mechanical pump. also thought about a cold air intake from outside the cab as I think the fuel is boiling in the carb. is the problem area. except for AV gas to solve the problem anyone else have any ideas. Thanks Martin

Welcome Martin, I would ask an expert on adding an electric pump on top of the existing mechanical pump. Too much pressure will have gas coming out of the carb and make your problem worse. I am guessing that your machine has the original straight 6 Ford engine?
 

Snowtrac Nome

member formerly known as dds
GOLD Site Supporter
Stop first the line between the fuel pump and carb needs to be steel, rubber wont conduct heat and the fuel in it stays warm and vaporizes. second an insulated base gasket is a good idea. the electric fuel pump will likely cause more problems a full flow fuel filter with a return to the tank will likely also help to keep fuel moving through the line and cool.
 

JimVT

Bronze Member
GOLD Site Supporter
I try not to run gas with ethanol. the ethanol increases the chance of vapor locks.
 

HankScorpio

Member
You need to shield the lines, especially from the exhaust. Chances are the fuel is warming up along its trip from the tank and is then boiling when it gets to the engine area. If the fuel line is run near the exhaust you might need to relocate things or shield the line quite a distance back from the engine. A non conductive spacer is a good idea too. Good fuel, as mentioned is important also.
 

pixie

Well-known member
SUPER Site Supporter
Spacers are $3-4 + shipping. Less than what an hour of my time would cost if I could find the right piece of wood.

These all fit my Ford 300/6. Carb studs spaced about 2.75". The one top/left is just like the one that was in there.

From QuadrajetParts.
 

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m1west

Well-known member
GOLD Site Supporter
Took it back to the mountain after installing a spacer under the carb and insulating the fuel lines. It ran pretty good on the way up but slowly over the hour trip the engine temp creeped up very slowly until it got to about 200 deg. and the electric fuel pump started knocking. ( vapor lock) I gave it a little more throttle and it went away and the engine never quit or faltered. The next day at the cabin I adjusted the ignition timing by advancing it by ear as I had no timing light. I must of added 6 to 8 degrees the vacuum advance moved nearly an inch before I called it good. it picked up 500 rpm so I adjusted the idle down again. Drove it a little and no sign of detonation or pre ignition. When I drove out it had 20% more power and engine temp. was at 185 deg. and no more vapor lock. next time out if I can make it before the snow melts ill remember the timing light.
 

rockhead

Member
So there I was, smugly sniggering at my not having this issue, chalked it up to serious header wrap job, then suddenly my smugness went away. Gonna have to my cat a southern belle name cuz she's got the vapors !
 

m1west

Well-known member
GOLD Site Supporter
So there I was, smugly sniggering at my not having this issue, chalked it up to serious header wrap job, then suddenly my smugness went away. Gonna have to my cat a southern belle name cuz she's got the vapors !

everything works against us in a carb. cat especially a cabover like Thiokol.
1-low gears high load=heat
2- engine in cab with no outlet for radiator fan except down=heat
3-winter gas=low vaporization
4-high elevation=low vaporization
 

PJL

Well-known member
This is why we had the 1200 retrofitted with a TBI EFI system. It wasn't cheap but the vapor lock issues are gone.
 

m1west

Well-known member
GOLD Site Supporter
This is why we had the 1200 retrofitted with a TBI EFI system. It wasn't cheap but the vapor lock issues are gone.

I have been thinking about that option. I think I have the problem resolved with the vapor lock issue. It has an electric pump in the engine compartment and thats the only issue I had last time. I plan to install a new mechanical pump as it is on the bottom of the engine where there is cold air and see if I can put more timing in it to further cool the engine while adding power. The performance of the EFI is great good starts and overall performance with more power and fuel economy but I want to try and keep it simple. You can file points, use an elevated gas can and gravity feed if the fuel pump goes out or a multitude of other things you can Jury rig to get home. You can't do that with EFI and electronic ignition. I have a modern snowmobile with EFI and all the bells and whistles. The first trip to the mountain guess what wouldn't start and stayed in the truck? and the old Thiokol vapor lock and all went up and back down.
 

mla2ofus

Well-known member
GOLD Site Supporter
Timing with not enough advance will make an engine run hotter, thus causing vapor lock. It also reduces power and decreases fuel mileage. Isn't there some way to get more of the heat out of the engine compartment? Maybe an electric fan pushing the hot air forward thru the radiator.
Mike
 

m1west

Well-known member
GOLD Site Supporter
Timing with not enough advance will make an engine run hotter, thus causing vapor lock. It also reduces power and decreases fuel mileage. Isn't there some way to get more of the heat out of the engine compartment? Maybe an electric fan pushing the hot air forward thru the radiator.
Mike

Thats what I mean advancing the ignition timing will add power and run cooler until it hits the limit of pre ignition or detonation that can be heard as a rattling noise when the engine is loaded or when you turn it off it wants to keep running. Using fuel with a higher octane rating without ethanol and a colder plug will help adding more timing without the rattle. You do not want to run in detonation that is a whole other problem ( broken rings, pounded down ring lands , cracked or broken pistons etc.) I used to race a boat that was run on methanol with a blower. 11 to 1 compression with 20# boost and 38 degrees of advance in the mag that is locked with no advance and no detonation. If you are running without any audible sounds of detonation but with a lot of ignition timing it is a good idea to run it under a hard load for short time then pull a plug and inspect the porcelain on the plug if there are small grey or black spots on it what is happening is a small amount of the electrode is burning up and inbeding in the porcelain (pre ignition) retard the timing a little and check it again. if you can see the electrode burning off you are lean on air fuel mixture or in detonation or both. No engine will survive that for very long.
 

m1west

Well-known member
GOLD Site Supporter
Timing with not enough advance will make an engine run hotter, thus causing vapor lock. It also reduces power and decreases fuel mileage. Isn't there some way to get more of the heat out of the engine compartment? Maybe an electric fan pushing the hot air forward thru the radiator.
Mike

the radiator idea might help but you would be cooling it with the air from the engine compartment and the head wind would not help either. I thought about moving the radiator forward and making a shroud that would deflect the hot air out to the sides not into the engine compartment using an electric fan. The more I read I think it is a common issue. I also think it is a much bigger problem today because of the reformulated gas. I have an old ford tractor that is gravity feed with marginal cooling that never vapor locks even at 110 out side. the difference is the engine is exposed and nothing gets heat sink. problem with the cat is how they designed the engine compartment but back in the day with different gas it may not have been a problem then. I am close to over coming it.
 

zspryte

Member
Site Supporter
My cat used to vapor lock on warm spring days after I ran it a bit and turned it off. I put an electric fuel pump under the cab between the engine and the rear-deck mounted tank. Ran a rubber fuel line from the pump to the carb and put aluminum shielding around the fuelline in the section directly over the engine. I also routed the line to minimize how much of it was over the engine. No more vapor lock. Rubber does not conduct heat (very well) so the gas temperature is about what is was in the tank. The aluminum wrap gives a little extra protection and is probably overkill.
 
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