I have an odd power loss problem-overheating? PROBLEM SOLVED

DonziGT230 · Last edited by DonziGT230 on Tue Nov 29, 2011 3:57 pm; edited 1 time in total

This is a stock single port motor in a sandrail. It has the stock pict 30, new 009 with compufire at 30ish degrees total adv., "off road" tins with no thermostat and remote adapted oil cooler moved outside, and an unbaffled trimill exhaust. It runs pretty well except that if I run it hard for more than a few minutes it starts dieing out like it's running out of fuel. If I ease up for a while it'll go strong again for a little while then start loosing power again. If I keep on it it'll eventually die. It'll restart struggling and if I'm mellow for a bit the power comes back. I was sure it was a fuel delivery problem 'till I checked; I have 3.5 psi and lots of flow. Plugs, valves, compression, etc. are all in spec. I'm wondering if the push rods are expanding faster than the cylinders and I'm loosing clearance.(?) Is that a common possibility? I've had it do this descending hills also which leads me to think the cylinders were maybe contracting faster than the pushrods at that point. It was pretty cool out, around 65-70F, and oil temp was always cool. I've had this car for a while and have experienced this a little bit, but it had so many other bugs to work out that I'd ignored it somewhat. Now that everything's together 'right' I finally got to lay into it hard and discovered this. I'm not apposed to loosening the valves a little to try, but wonder if there's just something else I'm not thinking of. I only get to run it on 'vacation' so I'm hoping to bring all the tools, parts, and knowledge I may need with me on the next trip. The valves are at .004, that's the spec I found based on my heads' stud type. The only other gripe I have is that it seems a little weak on power above 4K RPM, but assume that's just all this little restricted motor has in it.(?)
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modok · Posted: Fri Nov 18, 2011 5:47 pm Post subject:

are you driving on very rough terrain?

DonziGT230 · Posted: Fri Nov 18, 2011 6:01 pm Post subject:

Somewhere between rough and ludicrous most of the time, my chiropractor loves me going to the desert. The fuel tank was nearly as full as it could be so it shouldn't have been sucking air in case that's where you were heading.
_________________
I refuse to call a distributor a dizzy--earthquake.

The glass is always full and I can prove it!--me

modok · Posted: Fri Nov 18, 2011 6:14 pm Post subject:

If you shake the heck outa the carb it will run real rich and try to flood you out. Gets to the point you have to keep it halfway floored to keep it running. Once you stop bouncing around and let it run for a minute the extra fuel clears out and it runs ok again.

If that sounds like what it's doing, then I bet the poor stock carb just can't take the punishment Laughing

RockCrusher · Posted: Fri Nov 18, 2011 6:18 pm Post subject:

When I 1st started buggying I had a 34 pict and plugged the bowl vent and drilled/tapped for an outside the throat fitting with a tall hose that went up to the air cleaner. Cleaned things up a lot.

RC
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DonziGT230 · Posted: Fri Nov 18, 2011 6:21 pm Post subject:

That is a good thought, but it'll let me beat on it for a few minutes before it acts up at all and if I'm not hard on the power it's good all day even in crazy terrain and steep angles.
_________________
I refuse to call a distributor a dizzy--earthquake.

The glass is always full and I can prove it!--me

Slow 1200 · Samba Member Joined: July 02, 2004 Posts: 2130

I'd check the fuel line and the strainer at the bottom of the tank, sounds like it's starving for fuel

oh, check that the fuel tank vent works and you're not trying to create a vaccum in there!

DarthWeber · Posted: Fri Nov 18, 2011 7:57 pm Post subject:

DonziGT230 · Posted: Sat Nov 19, 2011 9:47 am Post subject:

While testing the pump I flowed out 1/2 gallon at a fast rate and it never slowed. Toward the end I popped the fill cap to make sure there was no amount of vacuum forming. The tins; well, 'off road' was a bad name, they're generic chrome. Actually only the upper is, the cylinder tins are the stock black pieces. The motor doesn't appear to be overheating; sound, smell, oil temp, all seem normal. I think I'll plumb in a fuel pressure gauge for my next time out so I can monitor it while running, maybe it's dropping. I guess it's possible that the pump has something that goes crappy after it gets hot. The only thing other than valves tightening I can think is maybe the venturi is icing, but that seems unlikely.
_________________
I refuse to call a distributor a dizzy--earthquake.

The glass is always full and I can prove it!--me

Hotrodvw · Posted: Sat Nov 19, 2011 9:53 am Post subject:

I was going to ask if you have an oil temp or cyl head temp gauge.....??

Fuel tank vent woul make it act up as well.
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jsturtlebuggy · Posted: Sat Nov 19, 2011 10:30 am Post subject:

Your are saying you have a 30 PICT carb, is it a round or square bowl?
If it is a square bowl installing the little plastic piece that hold the float piviot in place is backwards it can cause a running problem.
Also any debris on the needle valve inlet could cause not enough fuel to past through. Some times the rubber fuel hose has small pieces come off and can plug it.
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Fair Oaks/Orangevale, CA
Elrod Motorsports
Motion Tire Motorsports
Having fun with Dune Buggies since 1970
Into Volkswagens since 1960

DonziGT230 · Posted: Sat Nov 19, 2011 5:14 pm Post subject:

I have a round bowl. The hoses and filter are nearly new. I wish it were something that simple.
_________________
I refuse to call a distributor a dizzy--earthquake.

The glass is always full and I can prove it!--me

modok · Posted: Sat Nov 19, 2011 5:23 pm Post subject:

It could be carb related, but hard to say
I have not run one of those little carbs in years, but I did once opon a time. They worked good and solid but the whole thing is so small....... small bowl, small vent......................small inlet needle?
Could it be your needle and seat is too small?

jsturtlebuggy · Posted: Sat Nov 19, 2011 5:29 pm Post subject:

All it takes is sliding new hose on and a small sliver of rubber comes off and gets stuck in the inlet side of needle and seat and it get part way plugged so you never get enough fuel when running above an idle.
Remove 5 screws, use 14mm wrench to remove inlet valve and check.
Less than five minutes to find and fix.
_________________
Joseph
Fair Oaks/Orangevale, CA
Elrod Motorsports
Motion Tire Motorsports
Having fun with Dune Buggies since 1970
Into Volkswagens since 1960

DonziGT230 · Posted: Tue Nov 29, 2011 3:56 pm Post subject: Problem solved!

It turned out to be a little fuel filter screen in the carb inlet nipple full of gunk. The previous owner didn't have an inline filter so this was catching everything. I pulled it, cleaned it, and put it back in as a back-up to the inline.
_________________
I refuse to call a distributor a dizzy--earthquake.

The glass is always full and I can prove it!--me


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