new weber and backfire

gotago1

Legacy Registered User
City
wellsboro
State
pa
#1
Installed a weber 32/36 and right out of the box it ran smooth, but lacked acceleration, bogged 2nd through 4th, was barely able to hit 55 and bogged hard on hills. Checked timing, it was at 0 degrees BTC. Installed new plugs, timed to 5 degrees btc and set lean best idle and now it pulls great in first and 2nd but has a wicked carb back fire in 3rd and 4th. Especially on hills. Downshifting to 2nd stops the backfire. There is a mild exhaust backfire when i downshift. Any ideas?
 

gotago1

Legacy Registered User
City
wellsboro
State
pa
#2
Installed fuel pressure regulator set to 3.5 psi. Retarded timing to 4 BTC and now starts, idles, and runs good...no backfire. Idle mixture still lean best idle. Disconnected air pump belt and it ran some better. In third and 4th with a load on..climbing a hill or accelerating it runs smooth but seems to bog. I can barely hit 55 mph on a long stretch. The vacuum system is a mess, trying to figure out what to do with 5 port and 3 port cto's. EGR is plugged. I am thinking that the problem is somewhere in all the plugged up lines and ports that go nowhere. Its an 82 so i don't think it requires the nutter bypass. Any ideas would be appreciated. I need this thing as a daily driver this winter and want to get it as efficient as possible. Thanks.
 

CBRogers

Perpetual Parts Collector
LIFETIME
CJ-8.com Member
City
Yorktown
State
Va
#3
What distributor do you have on it????

If you are having a lot of vacuum issues you might want to really simplify what you have connected and use new lines. Old ones can be cracked and leak a lot.

If you have the cash an upgrade to a HEI style of Distributor will help out a lot. Simple 2 wire hook-up. The Davis DUI is the best but expensive at ~$300 there are China ones at ~$100.

Also it is a hotter spark and will let you open up the plug gap.

That Webber is very sensitive to too much fuel pressure.


Carl
 

cbford

Legacy Registered User
City
CLT
State
NC
#4
I think CBRogers is right on. Sounds like you need to work on your vac system. Leaks or a ported pressure/manifold pressure connection in the wrong place can cause all the symptoms you are fighting.
 

gotago1

Legacy Registered User
City
wellsboro
State
pa
#5
Thanks guys, I think your right. I'm going to put all new vacuum hose in. My egr and both 5 port and 3 port cto's are just there not connected to anything and not capped either. At idle the cto's aren't leaking. I was thinking that the switch may open up at higher rpm's and leak vacuum then? I'm just going to cap all of them off unless someone has a better suggestion. Should I just cap off the egr or try to plumb it back in? Thanks.

jim
 

mcmud

Legacy Registered User
City
on a hill
State
al
#6
The initial timing advance is set way low and it needs a bump, 49 state factory spec is 8*+ or - 1* at curb idle speed, and for all its worth the Cal. spec is 15*+ or - 1*. Weber recommends 10-12* BTDC, and I suggest that you give 10* a fair shot. That increase in advance will afford better pick up and added fuel economy.

The limited hi-way speed could be the result of one or more;
Inadequate timing advance... a low initial setting + restricted centrifugal advance will result in a sluggish flat line in acceleration/top end speed. Pull and look under the rotor, to the top of the distributor shaft you should find a felt pad. Apply several drops of oil, reset the rotor and twist it counterclockwise to verify that it will advance a few degrees and then allow it to snap back to the original position. If it fails to advance or snap back with authority its gummy at best, or seized in place. Repeated steps with the oil and twist may soon free the mechanism. The minimum amount of add on centrifugal advance spec is 13* at 2000 rpm. So if you select 10* initial you should see at least 23* at 2000rpm.

If you feel the engine stammer or hunt at the upper rpm range it will be due to restricted fuel flow.
May be cause of inadequate jetting but more often it is screw setting and may also be the result of the all too often problem of the FPR fuel flow restriction.

Tail pipe after-fire (backfire) is typically involving unburnt fuel entering the exhaust coupled with an exhaust air leak. Had the air pump been contributing at an inopportune time there is one major source of the air. Having the Air Injector manifold set with a leaky valve may still be contributing to the pop at the decel. The cause of the unburnt remains to be seen.

Neither of the CTO's are leaking air, they are a simple thermo valve awaiting use.

Inform me on which type of air filter is being used and I'll be glad to post and help in all respect with providing you with a fail safe vacuum system layout.

You've mentioned having the Weber dialed in to the lean-best setting.... where do you have the speed and mixture screw set.
 

scramblerjim

Legacy Registered User
City
vermilion
State
oh
#7
if you have that little cheap chrome regulator with a adjustment dial replace it with a holley regulator .advaned auto parts has them on the shelf. i called the weber tec support and was told the regulator was restricting fuel flow. put the holley on solved my fuel problem.
 

gotago1

Legacy Registered User
City
wellsboro
State
pa
#8
I have the chrome rectangular air filter. With the vacuum advance pulled and plugged I have the timing set at 6 degrees and 650 rpm, after reconnecting vacuum advance I back the idle down to 600 and adjusted mixture to approx 21 inches of vacuum (manifold vacuum). I also have the cheap (59$) dial-in fuel pressure regulator ste at 3.5...when I dialed it down to 2.5 the engine stiuttered pretty bad on hills and during acceleration. After I pick my kids up from school I will do all of the above and see what I come up with. Runs and idles great around town, but it's a slow crawl to highway speeds, unable to pull any rpm's in 4th, it doesnt stumble, it just drones on and on and doesnt accelerate. All I am running vacuum wise is the ported advance and the pcv...everything else is disconnected and plugged. I also removed the belt on the air pump. Thanks again for the advice, I'll let you know what comes of it.

Jim
 

mcmud

Legacy Registered User
City
on a hill
State
al
#9
I'll be looking forward to your report on any effect that the bump in the initial timing has had.

Before I post a vacuum diagram I'd like to chat with you with regard to a vacuum system that should prove to be of advantage.

With your having both a three port as well as a five port CTO is indicative of having been equipped with Heavy Duty Cooling. This system relied on Manifold vacuum signal for Vacuum Timing Advance at the startup and during engine warm up, converting to a "S" ported signal while the engine was at normal operating condition, then at any point in its operation if the engine started to overheat (which by the way was the design intent of ported vacuum, not that it was used to bring on excess overheating but rather to keep the engine exhaust hot enough to burn pollutants in the cat converter) it would revert back to the Manifold in order to cool it back down to the temp that ported vacuum was applied once more.

My suggestion is that you consider using Manifold exclusively, there are advantages with doing so.... unless your CJ is still equipped and or you have plans to maintain a Catalytic Converter.

Brings to mind that you've mentioned the EGR being disabled. If you have the Cat and have maintained a stock exhaust system the EGR is worth bringing back into operation. If there is no Cat and the exhaust has been modified to the standard of a more free flowing exhaust than the original system then that attempt would be futile.

To the Weber;
The means to complete satisfaction with this carb is to adhere to the Redline Weber Tune Guide.

In it you would see that the speed screw should not be turned inward more than 1-1/2 turn. And then that a lean best setting at the mixture screw should not exceed 2-1/4 turns out. The intent in this document is not to establish an idle speed as much as to evaluate the mixture strength to support the engine demand throughout the transition from the low speed circuit (idle speed thru 2000 rpm) into the high speed circuit.

A lean best setting is that which will cause a hiccup (slight lean misfire) at say every 10-15 seconds.

On the fully warmed engine and after a bump on the pedal, I urge you to set the speed screw and leave it at 1-1/2 turns in once the tip contacts the stop.

Then preset the mixture screw to say 3-1/4 turns out. At idle work that screw inward at no more than 1/4 turn an then allow enough time for that turn to have an effect to the idle quality then another, allowing time for that reaction, then another until a rather constant misfire occurs. Then work it outward at say 1/8th turns until that hiccup all but disappears... be patient as each adjustment to this screw will have an effect, if you allow the time between each tweak and if the throttle plate is closed to that preset or to the point that zero vacuum signal is evident at curb idle speed.

If you should need a Tune document give out a shout and let me know what your intent is with the vacuum system set up.
 

mcmud

Legacy Registered User
City
on a hill
State
al
#10
Your most recent description of the high end performance read more like a timing issue than it does fuel.
A restricted fuel supply will cause the engine to hunt while limited timing will cause it to "drone", or flatten out to the point of no more acceleration.

Scramblerjim offers a great suggestion with omitting that cheap'O FPR, he goes on with the idea to replace it with the Holley.... while I agree it is a much better choice I'll offer this; if you are running the OEM style fuel filter/regulator along with the factory fuel return line you should have zero need of an aftermarket FPR. If you were to ever see, feel or smell the effects of bowl overfill that excess pressure could bring-on, there is a Weber Viton needle assembly available for some 15 bucks that will omit any need of a FPR. It is part number 79519.200 and is available anywhere Weber parts are sold.

Here are three images that will help with plotting a timing torque curve.

The fist will indicate (yellow) that area that is almost impossible to read the scale at an engine speed in excess of 1500 rpm.

The second will show how to position the vibration damper so that you can apply a second timing advance indicating mark onto it,

The third will show how to read the initial + centrifugal advance. Due to the variances in vacuum advance it should not be considered as part of the total advance, so the advance tube should be disconnected and plugged while charting the Total Timing Curve. A separate one can be drawn with vacuum applied but since it is load dependent there is a better way of reading and applying it.

While at idle or just off of it use the original mark then as speed increases and that mark becomes hidden read the mark that you apply. As I mentioned at 2K rpm you should see at least 13* centrifugal advance and that added onto your initial selection. If you've the nerve to stay with it try to find the amount of advance at 3K.

Images are courtesy of John Strenk. Rip them and save them to your computer, they'll help others as well as they do you.
 
Last edited:

gotago1

Legacy Registered User
City
wellsboro
State
pa
#11
First of all I want to thank you for the excellent advice you've given me. Secondly, I'll update you on my progress. I pulled the cap and the rotor moves clockwise and snaps back but there is less movement counterclockwise but it does return when displaced. I oiled and worked the rotor several times and it does move more freely. I retimed it to 10 degrees BTC and it runs noticeably better but it still feels like I can get more out of it. I'll tune as per redline weber and see what I come up with. When I adjust the idle speed screw, if I come up with an idle speed less than scrambler book idle do i need to rejet or go with the new idle? The cat has been removed and this scrambler has A/C if that makes any difference. I also have another quirk, it starts on the the third attempt unless it has just very recently run. It's not hard to start, it just takes three attempts. Thanks again and I am looking forward to the vacuum diagram.


Jim Stephens
 

gotago1

Legacy Registered User
City
wellsboro
State
pa
#12
Minor setback...filled up today and fuel was pouring out of the 20 gl poly tank. Dropped the tank and the seat for the o-ring was damaged beyond repair and had been siliconed plus there was evidence of an old tank repair so I ordered a new 15 gallon metal tank. Hopefully it gets here tomorrow and I'm back in business.

Jim
 

mcmud

Legacy Registered User
City
on a hill
State
al
#13
Its a Jeep thing....

This layout will allow manifold vacuum advance at the start up and while the engine warms then would convert to "S" port vacuum during normal operating temperatures. This one utilizes the "E" port to control the charcoal canister. Advantage is that so many of them leak air so with this layout no signal could be lost in that instance at the vacuum advance mechanism while it is plumbed to the "S" port nipple. This one omits the three port CTO.

I'll follow up with a manifold vacuum advance layout (my preference and since you have A/C it would be yours as well) and if you should desire to try to restore the H.D. Cooling system give out a shout.
 

mcmud

Legacy Registered User
City
on a hill
State
al
#14
This is the one that I urge you to give an added bit of consideration.

It omits both CTO's, requires the minimum of tubes and you'll have the benefit of a cooler running engine with an added amount of rpm, this in itself would omit the urge to open the throttle to gain a higher idle speed and would certainly prove its worthiness when the A/C is keeping you cool.
 

gotago1

Legacy Registered User
City
wellsboro
State
pa
#15
tank is repaired and back in the jeep. I will experiment with vacuum and timing tomorrow and see what I come up with. Thanks.

Jim
 
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