I have a 78 dodge d100 with a 67 440 in it the engine has 906 heads, mopar 284/484 purple cam, msd coil, box and distributor, offenhauser dual quad intake, impco 425 propane carbs, forged crank and 6 pack pistons. it is missing quite a bit and has drivers side valve train noise. compression is 170 across all cylinders new NGK plugs and MSD 8.5mm wires does anyone know where i should start trying to find the problem

thanks

 

a -

Obvious stuff first. Are you sure the firing order is correct and there's no arcing between the wires and anything else?

What's your initial and total timing?

Does you MSD box have a rev limiter and could it be set too low? Could the box be defective?

Can you use a timing light to check each plug or visually inspect the plugs to find the culprit(s)?

After that's been sorted out (should be fairly quick), then go to the valve train. Are you using the stock rockers or are they adjustable and if so have they been adjusted correctly? Any chance of a bent push rod?


Sorry, not familiar with those carbs.

Welcome to the forum.

Archer

 

So when you say propane carbs I assume this means you are running propane as a fuel, or am I missing something? I would like to know more about this. I heat my home with propane and would love to be able to fill my tank at home. Probably don't work that way huh? There are several propane dealers near here. Is it cheaper than gas. I know it burns cleaner but is it colder too. How does that effect the tune?

 

ok first old distributor was 180 out so when we installed the new msd one we left it that way. all plug wires are correct timing is set at 10 or 15deg advance i believe ill double check later.

msd box has a 6000 chip in it have also tried a 3000 and it dosent fix it. i doubt the box is defective but is there any way to check or possibly the coil

the 3rd cylinder back on the drivers side is running about 130deg rest are almost 200

on the engine build sheet i have it dosent say much about rockers lifters etc but i know there not rollers im fairly sure there hydraulic

the truck runs on propane i just added that in case someone had any tips propane generally likes lots of spark advance

thanks

 

and yes you can convert any gasoline vehicle to propane or natural gas im not sure about filling from home though if you got a compressor you probably could

 

yes, propane as a fuel. Two 425 impco carbs on a dual quad intake. Runs just like it would on gas but starts with the first detonation and keeps the oil very clean. We fill up at gas stations where they fill BBQ bottles.

Any help on the miss? Put the timing light on all the plug wires this morning and all are sending spark. Started it with the valve cover off and everything seems to be moving like it should.

 

Just a guess ? Try re routing the plug wires, Put the dist back to where it is timed correct

 

"Missing." Is this a rythmic miss like one or two cylinders, or an erratic skipping, only at some rpms, etc? Describe the "miss" in more detail

The cylinder temp is telling, what does that plug look like as compared to others?

FIRST step is to run either a compression or leakdown test, or both if you can. Leakdown testers can be home fabbed, there are plenty of plans on the internet, Google it:

http://www.google.com/search?hl=en&s...l1878l1.8.3l12

Even if you don't have / can't make a leakdown tester, get a compression gauge that "snaps apart." you can then use the hose end, with the valve core removed, to hook to your air compressor. You can get each cylinder rotated to TDC, air it up, and listed for leakage in the exhaust/ carb/ and crankcase. This may give you some idea of where the compression loss is.

You might do a "backyard balance test."

Get some sort of probe, like your 12V test lamp, or a small screwdriver, and clip lead it to engine ground.

Pull the dist. boots up, and stick small nails/ brads down beside the plug wires into the dist. towers. Ground each plug individually and listen to the engine and watch a tach. The RPM should drop the same on each cylinder, and sound about the same. Low/ dead cylinders will of course not drop much or at all.

AND DO NOT discount anything. More than once I've seen a simple miss caused by a cracked spark plug which was not noticed.

 

switched around plugs and its still there

compression is 170 across the board and no leakdown

i think its lifters

any suggestions on what ones i should buy

 

and this miss is only on one cylinder as mentioned above, it is at all rpm's and causes the engine to idle at different speeds. i doubt its anything that would affect all cylinders it must be the lifters or a mouse in my intake manifold.....

 

Did you try doing the "balance test" I suggested? This would tell you in a second which cylinder(s) are not firing.

 

If you have one handy, one of those I.R. thermometers could help you locate the problem. The temp of the exhaust manifold/header will be different on the cylinder misfiring. Hotter in case of detonation or "lean". Or cooler in case of non-firing, or rich.