I'm just starting to trouble shoot this problem so any advice would be appreciated.

A friend of mine has a 1988 F600 with a 370 2v in it. There is a tag that the backfire mod was installed in 1990 and that the timing had been adjusted back then too.

I haven't checked the timing so far since I'm just getting started on it.

But here are the symptoms.

It has an overall rough idle. Seems to run really rich.

Needs to be choked to cold start and runs pretty rough when first started.

The back fire happens almost everytime the gas pedal is decelerated. Whether thats a quick pedal or slowing down for a stop sign.

About the only way you can minimize the backfire is to shift into neutral and use the brakes to slow down while very slowly allowing the engine RPMs to decrease.

If you just push the clutch in its going to have a huge backfire. Usually only about once and usually for sure less than 3 times which get progressively less severe.

This truck gets very few hi way miles, most of the time its just around the yard.

Just recently it was driven for about 1.5 hours oneway and back. And the radiator overheated on the way back.

I replaced the two thermostates and they did look like they might be shot. Just throwing that in in case it relevant to someones thoughts.

Thanks

 

Sounds like you may have a burnt valve or 2

 

So, I need to do a compression test? How do I verify/check for a burnt valve?