miss @>2000 rpm, need advice (1 Viewer)

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bsilva132

bsilva132

Joined
Jan 14, 2003
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Location
Wilton, Ca
I swapped in a 78 2F into my 74 FJ40 and am having issues with getting it dialed in. Specs- 78 2F, w/ tri Y header, non-USA dizzy, pertronix w/ flamethrower coil, new NGK spark plugs gapped to .41, rebuilt 74 cali carb w/ vac advance port (emmision vac tubes blocked off), valves have been adjusted, and it has 20inches of steady manifold vaccuum. Compression (warm) across the cylinders is 140/130/120/120/120. New head and manifold gaskets. I have set the timing to 7 degrees BTDC and 15 degrees BTDC and no matter what I have a miss @ >2000 rpm under load (mostly in 2nd on the SM420). I am going to pick up new cap, rotor, and plug wires tomorrow, but was wondering if anybody has any ideas as to what is causing the miss? When I rebuilt the carb I followed the main and slow jet sizes specified in Ed Cooks write up in the tech section except for the primary slow jet, it is 0.60 rather than the specified 0.50. The exhaust smells like it is running a little rich also. Any help would be greatly appreciated. Getting tired of it sitting in the grage and not being able to drive it.

-Brian
 
It depends on what kind of miss, so a more detailed description would help. If it is bucking and spitting back through the carb, it is more likely fuel starvation or lean mixture.

If it is just a ramdom misfire with no spitting and popping, it is more likely an electrical problem. Electrical problems can also be load sensitive and when they are they are voltage related because it takes a higher voltage to ignite a larger air/fuel charge. Things to consider would be insulation breakdown and an excessive spark gap. High voltage will always find the easy way to ground.
 
Hard to argue with PHead. I would stick a fuel pressure gauge between your fuel pump and carb and see what it reads. You should be getting like 4psi or so. If not, maybe fuel pump issue. Also, make sure there is no fuel pressure regulator in the fuel delivery circuit - no need for that with stock pump and carb.

I also had similar problem where it lost power in 2nd under load. Did all the other tricks others mentioned and it turned out to be a bad/stuck PCV valve. You said you capped off vac lines but I assume you know this one is still required. I replaced PCV valve ($2.50) and all is well. Just FYI so you can rule out the cheap and easy stuff first before you dig deeper.

AndrewT
 
PCV vale is still intact and is new. The miss is more of a stumble, I am pretty sure it is not bucking or spitting through the carb. I am picking up new cap/rotor/wires today and will reset the plug gap to stock specs. Thanks for the suggestions.
-Brian
 
OK. Check your distributor cap for any cracks - they could be very fine and small. Its another easy one to check and best to make sure. Even if you get new ones, its always good to know what the issue was.

I've heard this can cause similar issues.

AndrewT
 
Make sure your dist cap is on tight, my front clip had bent a little and the cap was not tight. I had a slight sputter (not sure what RPM I didn't have a tach then) my #5 plug also looked funky. #5 is on the front of the distributor, right where it was loose. I bent the clip in a bit and now everything is fine and dandy.

HTH
 
one maybe the dist is off by one tooth, or a leak in your intake/gasket, check that stuff.
 
Replace the cap, rotor, and wires; reset the plug gap to .39, replaced the positive and negative battery cables (w/ neg. to block and tub), and made sure the cap was down tight, but it still has a miss. Since I have a steady vaccuum I do not think I have a leak at the intake gasket. Since I have a 68 non-USA dizzy in a 78 2F, should the plug gap be set at .39 (2F) or .31 (F)?
 
I doubt if the plug gap would make difference in this range.

The first issue would be to determine whether it is carburation or ignition. Does putting the choke on partially help? If so, it may be a carb problem. Lean mix teends to make it buck and pop. Rich mix tends to waste gas and lower overall power, but not miss unless it is fouling a plug.

Electrical misses are more like what happens when you momentarily turn off the key. Things to consider might be: Is hte coil getting enough power (try hotwiring it). Coil, distributor, ignitor (not easy to check w/o replacing with known good components).
 
Did you try and operate it with the choke on like was suggested?

What did it do?
 
Since you rebuilt the carb, are you 100% sure that there is NOTHING in the float bowl, possibly clogging a jet?



This sounds like a fuel issue to me....
 
Dude,
You need to swing by Pigheads garage. It's in nearby Midtown Sacramento.
He's got a spare everything and is always willing to help a fellow 'Cruiserhead with adjustments.
 
What kind of fuel filter are you running?
Can you repeat the miss while parked? (with the hood up) and where is the fuel level in the porthole when it's missing? (just trying to rule out fuel delivery as an issue).
 
What size (main & secondary)jets you runnin' in that '74 carb?
Y'know, you really oughtta get in touch with Pighead...you guys are runnin' almost the same engine. 'Cept he's got a cam...
 
Sorry Pig and Poser, I somehow missed your posts to this thread. I am going to try and meet up with Pighead on Wednesday.
 
what vac lines are still hooked up? I have a similar semi-unsolved problem, result of going back to stock carb on a 75, not knowing where the vacuum lines went, had the power valve unhooked, so it smelled gassy and ran crappy, the AAP was hooked up to manifold vac, though, put a tee in, so that AAP and power valve were both hooked up, started good, ran like yours with a big crappy spot, but smooth low RPM, good high RPM, blocked off AAP, ran great! so that might be worth looking at. funny thing is that the truck STARTS a lot better with the AAP connected, RUNS better without it. not sure what the solution is there. also not sure how similar our carbs are.

so in the image here, disconnect the bottom bit that's circled, make sure that the top one is connected, and see if that helps. it might start crappy when cold if bottom one is unhooked. if this is your problem and you find a way to have it start AND run good, let me know, please!!
-stefan
image stolen from here:
http://www.sor.com/sor/cat042-carbp...retion&descriptionpg.ctx=Page 042 Carburetion
carb.JPG
 
When? Yesterday Wednesday or next week Wednesday? How 'bout this weekend?

bsilva132 said:
Sorry Pig and Poser, I somehow missed your posts to this thread. I am going to try and meet up with Pighead on Wednesday.
Click to expand...
 
Pretty sure bsilva132 said he rebuilt his '74 carb...
Kinda similar, on the inside, but no AAP or any of that other circled stuff.

gladly said:
<snip> also not sure how similar our carbs are.

so in the image here, disconnect the bottom bit that's circled, make sure that the top one is connected, and see if that helps. it might start crappy when cold if bottom one is unhooked. if this is your problem and you find a way to have it start AND run good, let me know, please!!
-stefan
image stolen from here:
http://www.sor.com/sor/cat042-carbp...retion&descriptionpg.ctx=Page 042 Carburetion
Click to expand...
 
right you are, darn, I was hoping that i'd find a solution to my problem via his thread, oh well.
 
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