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Unread 10-14-2008, 08:28 PM   #1
CrazyHorse6
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MC2100 / 258 question

Sorry for another long MC2100 thread, but I couldn't find the answer I needed.
I have the 258 with the MC2100 1.08, TFI upgrade, timed with a light to 8 degrees BTDC, I believe I have my mixture screws set properly as I'm getting a steady 19 of vac at idle, and until today it was running pretty well, just too rich. Before today I was running #49 jets (I'm at about 800' above sea level) with a 6.5 power valve.
As said, it was running well just rich so I read that #47's or #46 jets were optimum and so I picked up a set. I put in the #47 and went for a test drive - result was an intial surge of acceleration and then it immediately stumbles, and unless I back off the throttle, it dies. Once I baby it up to speed, I can maintain speed but jumping on the throttle results in a stumble. After reading several threads, I suspected the 6.5 power valve but the thing throwing me off was I was running fine until I put #47 jets in. My carb came with two other power valves - another 6.5 and a 7.5 but I can't tell which is which (one has a F.7.5.6 and the other a A.3.5.7) The A.3.5.7 couldn't even make it up the hill in my driveway so I'm assuming the other was the 7.5 and that I was at least headed in the right direction.

My question, assuming everything else is fine (no vac leaks, EGR is ok, choke functioning properly, good timing, etc), should I really be running #47 jets and if so, is the 7.5 power valve is not the right one? Do I need a 8.5? I've heard two ways of determining what type of power valve you need based on vac, but I don't know which to use.
Thanks and sorry for the long thread.

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Unread 10-14-2008, 10:00 PM   #2
CrazyHorse6
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Update:
After looking on Walker Fuel system's website, turns out part of my problem is that the Ebay guy who sold me this Carb and power valves sent a 3.5hg (A.3.5.7) and told me it was a 6.5. That explains why I couldn't get out of the driveway with that power valve.

He also told me to verify what power valve I need by doing the following - take idle vac, divide by 2, then subtract 2 and thats the magic number- so my vac is 19, divided by 2 is 9.5, minus 2 puts me right back at 7.5 which doesn't seem to work.

Any help is appreciated.
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Unread 10-15-2008, 06:37 PM   #3
CrazyHorse6
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I'm really hoping someone can point me in the right direction here. I picked up two new Power valves - a 8.5 and a 9.5 based on some information on other threads but neither seem to change my symptoms.... a very short bit of acceleration and then a bad stumble followed by a recovery. I noticed that when I remove the air filter and cup my hand over the choke butterfly, when I blip the throttle there is almost no hesitation. I also noticed that if I spray carb and choke cleaner down the throat right when I blip the throttle, there seems to be less hesitation. Does this mean that on its own its not getting enough fuel?
Also, I've played with the accelerator pump linkage and no matter what I do there (top hole, middle, bottom) it makes no difference to the stumble.
This is driving my crazy -any help is appreicated.
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Unread 10-15-2008, 10:21 PM   #4
coas
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Set your timing with a vacuum gauge first.
Try using
for more tip.
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Unread 10-16-2008, 07:42 AM   #5
CrazyHorse6
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Coas,
thanks for the help. I'm pretty confident in the timing and I've already verified it again just to be sure. I also downloaded and read through that link - thanks. Despite mine being a MC2100, the model covered in that article is quite different as are the engine types for all the specs, so it doesn't seem to solve my problem. I think what I need is a good troubleshooting guide - if your carb does this *, then do this*.
I've ready nearly all the MC2100 threads on the forum and followed the advice but I'm still having issues. The Ebay guy I bought this thing from tells me that #47 jets are too small but his #49's run too rich. The threads all suggest (to include the article link you sent) to use a 8.5 or a 9.5 power valve, but the Ebay guy suggests a 6.5.
Well I tried all kinds of combinations - 47's with a 6.5, 7.5, 8.5 and a 9.5, 46's with all 4 power valves, and finally I have the 49's back in with a 6.5 power valve - this is the only combination that runs somewhat well. I've read about 3 different ways to determine your power valve and all three point to a diffent sized valve.
When I kicked this whole thing off I was running decently well and had no stumble, just ran rich with #49's and a 6.5 power valve.

Lastly, someone did suggest using ported vac as opposed to Manifold vac - can you confirm which to use? I don't have any manifold vac connections on my manifold - its an old clifford 6=8.
Thanks
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Unread 10-16-2008, 10:43 AM   #6
Mike Romain
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A bad EGR valve or badly plumbed one can cause a hesitation like you have that a richer mix may compensate for. If you still have one, I would unplug it, plug it's line and see. If it is unplugged I would verify it still has a strong spring load closed. I have seen them fail and flop causing hesitation and bogs.

The long intake manifolds are also notorious for leaking and needing a second torque after an install and run cycle. I would carefully spray some WD40 or carb cleaner along the gasket at the head and the carb base looking for a stumble.
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Unread 10-16-2008, 10:49 AM   #7
coas
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There are few differences in the carb but the principles applies.
I'll say it again, use a vacuum gauge, the harmonic balancer, damper, is made of two metal rings with a thin rubber layer in between, when it get old the outer ring, where the timing mark is, slide over the rubber. When this happens you can't use a timing light anymore until you change the balancer.

The symptoms suggesting lack of fuel when accelerating, late PV or late acc. pump, probably the PV. see if it blowing black smoke after accelerating, when recovering.

I've installed a few of this in the past and all were fine with 48 jets and 8.5HG PV (for stock 258). If you don't have 48 lower the float to 0.55inch as explained in the file.

Use the 8.5HG PV but make sure you apply some medium strength thread locker on the thread and gasket. let it cure for an hour or two.

Make sure the vacuum port for the choke on the carb base is blocked with epoxy.

Take off the acc pump cover and the venturi booster and make sure the passage is not clogged. Careful there, there is a small metal ball and weight under the booster venturi, do it off the engine. Clean the booster venturi while you're there.

You need ported vacuum for the distributer from the port under the choke, nothing else. check if there is a corresponding movement at the dist when you hit the throttle.
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Unread 10-16-2008, 11:26 AM   #8
CrazyHorse6
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Quote:
Originally Posted by Mike Romain View Post
A bad EGR valve or badly plumbed one can cause a hesitation like you have that a richer mix may compensate for. If you still have one, I would unplug it, plug it's line and see. If it is unplugged I would verify it still has a strong spring load closed. I have seen them fail and flop causing hesitation and bogs.

The long intake manifolds are also notorious for leaking and needing a second torque after an install and run cycle. I would carefully spray some WD40 or carb cleaner along the gasket at the head and the carb base looking for a stumble.
Mike, thanks for the help. I was concerned about the EGR valve, which is on mine I believe mounted directly to the side of the engine. There are no hoses running to it at all and all ends are capped. I've sprayed choke cleaner all around it (and everywhere else for that matter) and the RPM's don't change, so I don't think its leaking. Are there any other ways to check it?
I also re-torqued the manifold about 3 weeks ago and no bolts turned, so I don't believe I have a problem there. Any other ideas? Do you have a recommendation for what size jets and power valve a 258 at around 750' above sea level with the team rush ignition should be running?
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Unread 10-16-2008, 11:38 AM   #9
Mike Romain
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Quote:
Originally Posted by CrazyHorse6 View Post
Mike, thanks for the help. I was concerned about the EGR valve, which is on mine I believe mounted directly to the side of the engine. There are no hoses running to it at all and all ends are capped. I've sprayed choke cleaner all around it (and everywhere else for that matter) and the RPM's don't change, so I don't think its leaking. Are there any other ways to check it?
If there is a pin under it entering the exhaust side, I would reach under on a cold engine and push the pin into the diaphragm or away from the exhaust to be sure it is nice and tight.
Quote:
I also re-torqued the manifold about 3 weeks ago and no bolts turned, so I don't believe I have a problem there. Any other ideas?
It still can't hurt to spray it. Gaskets do blow chunks now and then. Same for the carb base.

Quote:
Do you have a recommendation for what size jets and power valve a 258 at around 750' above sea level with the team rush ignition should be running?
I think you are bracketing it now, but would want to verify something isn't causing it to lean out.
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89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
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Unread 10-16-2008, 11:39 AM   #10
CrazyHorse6
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Quote:
Originally Posted by coas View Post
There are few differences in the carb but the principles applies.
I'll say it again, use a vacuum gauge, the harmonic balancer, damper, is made of two metal rings with a thin rubber layer in between, when it get old the outer ring, where the timing mark is, slide over the rubber. When this happens you can't use a timing light anymore until you change the balancer.

I'll have to read up on using the vacuum gauge for timing - I don't know how to do it and unfortuantely I don't understand the concept you explained. Sorry about that. I just used a light for the timing and a vac gauge for the idle mixture screws.

The symptoms suggesting lack of fuel when accelerating, late PV or late acc. pump, probably the PV. see if it blowing black smoke after accelerating, when recovering.

I don't have any black smoke during acceleration and it definitely smells leaner than it ever has. I thought it was a lack of fuel as well, but even with a 9.5 pv and #47 jets it wouldn't run w/out a stumble.

I've installed a few of this in the past and all were fine with 48 jets and 8.5HG PV (for stock 258). If you don't have 48 lower the float to 0.55inch as explained in the file.

I have #48's coming as well as another 6.5 pv from the Ebay guy- I'll try the 48's with the 8.5 like you suggested. I may have been under estimating just how much of a change you get from 47's to 48's to 49's. I also need to measure my float - that was another item I have not changed as I just left it as he sent it to me.

Use the 8.5HG PV but make sure you apply some medium strength thread locker on the thread and gasket. let it cure for an hour or two.

Will do

Make sure the vacuum port for the choke on the carb base is blocked with epoxy.

I could not find that hole on my carb base - will look again.

Take off the acc pump cover and the venturi booster and make sure the passage is not clogged. Careful there, there is a small metal ball and weight under the booster venturi, do it off the engine. Clean the booster venturi while you're there.

Oh boy...

You need ported vacuum for the distributer from the port under the choke, nothing else. check if there is a corresponding movement at the dist when you hit the throttle.
thanks VERY much for the details - I really want to get back on track with this thing.

Last edited by CrazyHorse6; 10-16-2008 at 11:54 AM..
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Unread 10-16-2008, 12:07 PM   #11
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Quote:
Originally Posted by Mike Romain View Post
If there is a pin under it entering the exhaust side, I would reach under on a cold engine and push the pin into the diaphragm or away from the exhaust to be sure it is nice and tight.


It still can't hurt to spray it. Gaskets do blow chunks now and then. Same for the carb base.



I think you are bracketing it now, but would want to verify something isn't causing it to lean out.

Thanks Mike -
I did spray the manifold - no rise in rpm. I checked for the pin on what I thought was a ERG valve - no pin. Just three capped ports all facing up. The valve in quesition is screwed in right on the side of the engine beneath the manifold.
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Unread 10-16-2008, 12:12 PM   #12
Mike Romain
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Quote:
Originally Posted by CrazyHorse6 View Post
Thanks Mike -
I did spray the manifold - no rise in rpm. I checked for the pin on what I thought was a ERG valve - no pin. Just three capped ports all facing up. The valve in quesition is screwed in right on the side of the engine beneath the manifold.
The EGR would be on the exhaust right below the carb. That was the CTO you were looking at. It, the CTO is still needed to turn on the gas tank vent. Most CJ's won't run well without a gas tank vent, they can bog out bad to the point of running out of gas on the highway.

Check this link out for the EGR: http://www.jeepforum.com/forum/f8/cj5-258-vacuum-diagram-544546-post5074772/
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Unread 10-16-2008, 01:03 PM   #13
CrazyHorse6
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Quote:
Originally Posted by Mike Romain View Post
The EGR would be on the exhaust right below the carb. That was the CTO you were looking at. It, the CTO is still needed to turn on the gas tank vent. Most CJ's won't run well without a gas tank vent, they can bog out bad to the point of running out of gas on the highway.

Check this link out for the EGR: http://www.jeepforum.com/forum/showthread.php?p=5074772
Well that explains why I can't find it - I don't have one. The PO may have pulled it years ago as I don't recall ever seeing it. I don't have emissions testing in GA due to the age of the Jeep, so is that something I need? Missing it isn't the cause of the problem is it?
Thanks again for all the help!
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Unread 10-16-2008, 01:18 PM   #14
Mike Romain
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Quote:
Originally Posted by CrazyHorse6 View Post
Well that explains why I can't find it - I don't have one. The PO may have pulled it years ago as I don't recall ever seeing it. I don't have emissions testing in GA due to the age of the Jeep, so is that something I need? Missing it isn't the cause of the problem is it?
Thanks again for all the help!
If you don't have it you don't need it.

What is venting your gas tank now? That also shouldn't be your issue, but if in doubt, cracking open the gas cap will relieve the vacuum if any has built up. It it goes whoosh when you open the cap, well...
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89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
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Unread 10-16-2008, 01:53 PM   #15
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My gas tank vents through a hose just below the filler nozzle and through a return line to the charcoal canister I believe - been so long since I dropped it - but it doesn't whoosh when I open it fortunately!

This thing is driving me nuts - I just went for a drive during lunch - I'm back to the original setup in which I recieved the carb - #49 jets and a 6.5 power valve - and I'm stumbling all over the place.

The only thing different now vs 3 days ago where it was ONLY running rich is a slight change in where the accelerator linkage rod is. I swear its back in the same place but the nut that locks it in may be off by a few turns in our out. Either way its set to make just slight contact with the plunger on the accelerator pump with the throttle at neutral, and then when you punch it, sure enough it depresses the plunger - I can see the shot of fuel squirt out down inside the carb as well. I get about 1/2 second of acceleration, then a signficant stumble, and then a recovery of acceleration. I tried some extremes with the linkage - bottom hole - ran horrible - top hole - ran horrible - middle hole, slightly less horrible. How fine tune of an adjustment is the linkage setting? Anyone know where it should be? There is a nut that threads onto the end of the rod - pulls the linkage closer and further away from the plunger as you thread it in and out. Here are some pics - pardon the crude "accelerator cable linkage".
[IMG][/IMG]
[IMG][/IMG]


Coas suggested putting in 48's with a 8.5 power valve - I'm going to do that tonight and see what happens.
Thanks for all the help guys - I owe you both a beer - actually I owe you Mike many beers for help in the past - think its a 24 pack by now.....
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