The Runner Stumbles... at 1,250 rpm.

[720inOlyWa]

Forgive my obscure movie reference there. Nobody is gonna get it. But maybe, just maybe, you will have some insight into my last remaining obstacle to perfectly smooth vehicle operation.

 

Imagine an 85 720 NAPZ King Cab that runs and drives just fine. 7,000 miles on a lot of engine rehab. Smooth operation through all gears, easy starting, all of it. Sure, the 32/36 weber makes it a tich cold blooded, but once it is cleaned out and running, solid as a rock. Only one real quirk remains, and it baffles me.

 

When warmed up, if I am idling at a light at 800 rpm, it is smooth as silk. If I apply enough pressure to slowly begin raising the rpm, a misfire creeps in at around 1,100 to 1,200 rpm. Leaving the very slight pressure on, it sort of stumbles through 1.250 and cleans up again at about 1,400 rpm.

 

Oh, I have been tweaking the idle mixture screw enough to think I am pretty much on the money. (Not to say I am dead right tough...) I ordered a new plug wire set, just because I wanted to replace them as a base line anyway.

 

It seems to me that it is in the timing and the way the distributor is- or isn’t- advancing properly. There isn’t really any significant play in the distributor shaft, and the only service to the distributor that I have done so far is to put on a OEM cap and rotor. I know that the timing is spot on 3 degrees.

 

It is as if the handoff between idle and power mode is not quite going smoothly, right at 1,250 rpm. Any ideas?

 

Thanks! 

[Brohemius]

Is that a logans run reference?

 

Also how new is your carb? It could be dirty jets or something carb related if you have any age on the weber.

 

Though now that i re read, you say it misfires... So im probably wrong haha.

[720inOlyWa]

Carb is brand new, hard to believe it is dirty jets already. Maybe that’s why you are right though...

[650savag]

You may find some good ideas if you read the posts in the thread titled: "Replaced Hitachi with a new Weber" in the "engines" forum. I was experiencing a similar stumble after installing the new Weber and finally got it out by advancing my timing to 15 degrees and changing out the primary idle jet from a #60 to a #65. I actually enlarged the jet to a #65. My L20b engine wasn't actually misfiring but was bogging a little when I would first start to give it has. You could have a vacuum leak also if you recently installed the carb. You probably know how to use carb cleaner to spray around the base of the carb and adapter plates and intake. I had a lot of trouble getting my 32/36 to seal and had to remove it 2 times and reinstall it. I had to wind up lapping the surfaces of the adapter plates flat and using gasket sealer on the gaskets.

[datzenmike]

You could definitely try more advance but not 15 degrees. The NAPS Z24 uses dual plugs and the burn time is much reduced as the 3 degrees advance shows. Factory setting states 3 degrees + - 2 degrees for variations in gasoline, temps and altitude. Give it a try.

[Charlie69]

Most Webers out of the box will have this stumble.  Get a set of jets and see what works.  Webers are altitude sensitive.

 

My King Cab at this moment does not stumble but it is idling ruff.  I need to richen the idle mixture after going through emissions testing.

[720inOlyWa]

DAMMIT-THIS IS WHY RATUSN ROCKS!

 

I literally turned off the engine and stomped right in here to thank my thread respondents. Thank you!

 

I found the problem, thanks to a few words that got me to thinking...  You see, I used a propane torch (unlit, of course) to see if I was getting any vacuum leaks. I didn’t find a one. And then, someone mentions that you use carb and choke cleaner instead because the cooling fan blows the gas away from the leaks.  Huh. Makes sense, don’t it?  So I timed her up this morning  as Mike suggested and gave the carb / choke cleaner technique a try. Holy shit- it cleaned right up! It is leaking around the base- ALL around the base- of the carb! Oh man.

 

The moral of the story is that I thought I had performed a good test for leaks the way I was shown, maybe 40 years ago, using a propane torch (unlit, of course). But another person has a different (and much better) way to test for leaks and posts it. I try that. Problem solved. I could have gone on for a long time looking elsewhere for solutions, thinking I had already covered the leak test base, but instead, I get a direct route to ‘problem solved’. Maybe this is a small thing, but in my experience with machines, it is often one, two or three small things that create the larger problem. And that one little bit of information that I was missing- to use carb cleaner- made all the difference.

 

I’ll re-check the timing once the carb is sealed properly. 

 

Awesome! Time to re-seal the carb- one more (last?) time!  Thanks again!

 

Whew, it is such a high to know exactly what the problem is and how to fix it.

 

 

Epiloge: WHAT A GREAT TEST DRIVE!

[bananahamuck]

It almost makes it worth it to put up with all the jerk-offs on here. 

 

 

almost

:lol:

[720inOlyWa]

Epilogue / epilogue:

So I just did the same thing to my 4x4 truck and it also started right up and ran real nice- except for a tiny squeal coming from the pully bearing down on the A/C compressor. No big deal- I can deal with that later. First, how abut taking our first ever test drive?!?

 

So the first thing I notice is that the clutch is very touchy, not soft at all. First gear is fine, second is okay too, third gear is.... really crunchy! It sounds like some real bad shit is going on in the transmission in 3rd gear! I shifted down to 2nd and no big noises. I crept back to my driveway in 2nd.

 

Well, that simplifies things a lot! I parked the 4x4 under a tree and will get back to it later, much later, when I have either formulated a plan or chanced upon a 5 speed 4x4 transmission or a good resource for rebuilding this one.... Bummer.

[datzenmike]

Doesn't necessarily have to be from a 4x4. A 2wd transmission will still work. Only difference (well, other than the gears are closer together) is sealing up the speedometer cable. On mine I cut the screw on end from a cable, RTV's the opening closed, when cured just screwed it on over the speedometer pinion sleeve.

[720inOlyWa]

Doesn't necessarily have to be from a 4x4. A 2wd transmission will still work. Only difference (well, other than the gears are closer together) is sealing up the speedometer cable. On mine I cut the screw on end from a cable, RTV's the opening closed, when cured just screwed it on over the speedometer pinion sleeve.

 

Thanks, Mike. I erealize that you cannot diagnose this- or any- problem very effectively based upon my post, but I am very curious about what your plan of action would be in this case. Any ideas about what happened to third gear? Surely the transmission has to come out, and it is clear it has to come out through the hood. But what then? Does one rebuild the transmission, or replace it? And if I found another, wouldn’t I need to rebuild that one anyway, just to be safe?

 

Rebuilding the transmission is way ‘out of my network’, in terms of mechanical experience, but a friend who has been there told me it isn’t that bad at all. We have a local transmission shop, and I suppose it is a lot less expensive if you take the transmission to them out of the car, but the last work I had done there was unbelievably expensive.

 

I am one of those fucking Irish types who, once they get the bone in their teeth, cannot let go t save their life. When I heard that crunchy gear, I probably got more committed, not less. I put a windshield in this truck, so I am damn well gonna fix the transmission too! I just have no idea how that is going to happen as of this post. Any insights, advice, directions towards information, would be greatly appreciated.

[720inOlyWa]

Doesn't necessarily have to be from a 4x4. A 2wd transmission will still work. Only difference (well, other than the gears are closer together) is sealing up the speedometer cable. On mine I cut the screw on end from a cable, RTV's the opening closed, when cured just screwed it on over the speedometer pinion sleeve.

 

How much difference is there in the ratios? I have a good 2WD transmission in hand now and it would be great to be able to use that n my 4x4, if reasonable. Also, what about the speedo cable arrangement, since you capped it?

 

Many thanks.

 

Marc

[Lockleaf]

In the 4x4 speedo cable goes to the transfer case and the transmission doesn't even have a hole for one. If you use a 2wd trans, you just plug that hole and continue using the one in the transfer case like normal. A little Google research into "720 gear ratios" should net you the rest of the info you need

[720inOlyWa]

In the 4x4 speedo cable goes to the transfer case and the transmission doesn't even have a hole for one. If you use a 2wd trans, you just plug that hole and continue using the one in the transfer case like normal. A little Google research into "720 gear ratios" should net you the rest of the info you need

Ahhhh, I see it now. This is great news! Thanks!

[Charlie69]

DAMMIT-THIS IS WHY RATUSN ROCKS!

 

I literally turned off the engine and stomped right in here to thank my thread respondents. Thank you!

 

I found the problem, thanks to a few words that got me to thinking...  You see, I used a propane torch (unlit, of course) to see if I was getting any vacuum leaks. I didn’t find a one. And then, someone mentions that you use carb and choke cleaner instead because the cooling fan blows the gas away from the leaks.  Huh. Makes sense, don’t it?  So I timed her up this morning  as Mike suggested and gave the carb / choke cleaner technique a try. Holy shit- it cleaned right up! It is leaking around the base- ALL around the base- of the carb! Oh man.

 

The moral of the story is that I thought I had performed a good test for leaks the way I was shown, maybe 40 years ago, using a propane torch (unlit, of course). But another person has a different (and much better) way to test for leaks and posts it. I try that. Problem solved. I could have gone on for a long time looking elsewhere for solutions, thinking I had already covered the leak test base, but instead, I get a direct route to ‘problem solved’. Maybe this is a small thing, but in my experience with machines, it is often one, two or three small things that create the larger problem. And that one little bit of information that I was missing- to use carb cleaner- made all the difference.

 

I’ll re-check the timing once the carb is sealed properly. 

 

Awesome! Time to re-seal the carb- one more (last?) time!  Thanks again!

 

Whew, it is such a high to know exactly what the problem is and how to fix it.

 

 

Epiloge: WHAT A GREAT TEST DRIVE!

 

Propane is heavier than air so even with out the air flow from the fan it does not work for this purpose.