22 replies to this topic

[nspr]

Just to bring my own old thread back from the dead for future reference.
To describe how intermittent this issue has been, on some occasions just lifting off and applying tbrottle again would solve the issue. I went on to replace most of the ignition - dizzy, coil, etc.
I've come to the conclusion this was multiple issues giving common effect, that of the sudden reduced power when applying more than a given amount of throttle. Firstly, poor carb setup and timing being out. Second, bad earths both at the battery and engine. Third, a bad thermostat stuck open causing the engine to run cold at speed.
Earth seems to have been the main thing. Cleaned up the battery terminals, replaced the engine strap and put some star washers in to ensure a good chassis contact and that seems to have helped enormously.

Edited by nspr, 02 August 2026 - 04:13 PM.

[68+86auto]

For the earth to make a difference, it must've been cranking poorly too. There is a reason the diagnostic process should almost always start with testing the starting and charging systems.

[mbolt998]

It's possible that it's the needle valve that lets fuel into the carburettor float chamber. Those can sometimes stick a bit causing intermittent fuel starvation. I guess you could inspect it and give it a clean.

[nspr]

Just my luck that after posting this the same problem is back, so yeah, not earth now.

Started slowly and again intermittent, so decided to take it into the back field and give it a good run to test it.

Promptly completely conked out, I think on a small bump in the field.

Usually when running normally the fuel filter has a small pocket of air near the top and is visibly flowing. I noted when this happened again at one point, the filter was completely full of fuel. 

Would an issue in the carb like a blockage potentially cause this if the pump is still trying to force the fuel through?

This time, when it's completely conked out, the level in the filter is just below the exit. I did wonder if the pump could be the issue, so tried putting the car in a high gear and pushing it to turn the pump. Didn't achieve anything.

I ended up getting the car running enough to get it out the field and out the way in the yard by using the choke as a throttle, but it had an extremely lumpy idle and applying any actual throttle immediately caused the revs to drop as it bogged down.

 

Is it possible a small bump has dislodged something in the carb?

Edited by nspr, 04 August 2026 - 01:25 PM.

[nspr]

It's possible that it's the needle valve that lets fuel into the carburettor float chamber. Those can sometimes stick a bit causing intermittent fuel starvation. I guess you could inspect it and give it a clean.

Any recommendations on a good guide to cleaning a HIF38? Think you're on the money here.

[nspr]

Changed battery to a larger item & tightened fanbelt this eve. Took the air filter off, manually cycled the piston in the carb, moved fine. Then refit filter, started, problem gone. Drove a short distance at low throttle, no problem. Put your foot down, immediately dies. Take suction pot off carb, check jet / piston, seems fine, reassemble, runs fine. Gice it some throttle, dies. Once it's died again it can only be restarted with lots of choke, dies immediately if choke is removed or throttle applied. Checked if piston stuck, seemed to move fine, topped off dashpot, runs fine again. Give it some throttle, dies. Completely stumped. Have ordered a carb rebuild kit so have a project.

[68+86auto]

Changed battery to a larger item & tightened fanbelt this eve. Took the air filter off, manually cycled the piston in the carb, moved fine. Then refit filter, started, problem gone. Drove a short distance at low throttle, no problem. Put your foot down, immediately dies. Take suction pot off carb, check jet / piston, seems fine, reassemble, runs fine. Gice it some throttle, dies. Once it's died again it can only be restarted with lots of choke, dies immediately if choke is removed or throttle applied. Checked if piston stuck, seemed to move fine, topped off dashpot, runs fine again. Give it some throttle, dies. Completely stumped. Have ordered a carb rebuild kit so have a project.

 

Check the fuel pressure when it happens using a T piece.

Edited by 68+86auto, 04 August 2026 - 10:26 PM.

[mbolt998]

 

It's possible that it's the needle valve that lets fuel into the carburettor float chamber. Those can sometimes stick a bit causing intermittent fuel starvation. I guess you could inspect it and give it a clean.

Any recommendations on a good guide to cleaning a HIF38? Think you're on the money here.

 

I would just take the little needle out and clean it and the seat it goes into with whatever you have. Acetone is good. Or spray some carb cleaner if you have it. I think a clue this might be the problem is there is sometimes a kind of wear line around the needle where it goes into the seat. I'm not referring to the main needle in the SU here (just to be clear) but to the needle valve in the float chamber. Let's see if I can find a diagram... Yes this thing I've circled in red.

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Edited by mbolt998, Yesterday, 11:27 AM.