86 258, carter bbd, nutter bypass (distributor controlled by ported vacuum)
been working hard to achieve the near-mythical performance from this engine that mike romain describes in his comparable rig: namely third gear tire smoking power and 30 mpg in heavy traffic ;)
I can't seem to find a timing advance that my engine likes throughout its power curve. I have tested everything from 4 to 12 btdc. The symptoms I am still getting are somewhat sluggish acceleration at full throttle (actually does pretty well at half to three quarters throttle) and what I can only assume is some detonation (sounds like a metallic buzz? under load) regardless of the timing setting. I haven't advanced it much more than 12. I have also noticed that once the mechanical advance takes over (higher rpm) the torque becomes downright snappy, which makes me think that it may have something to do with the ported vacuum advance that controls it up until then... Any thoughts?
(I have replaced the fuel filter and checked my carb settings)
I would recommend you try it with the EGR line off and blocked. I have a dead spot with the egr working. I also think there is a delay valve in the EGR line that can be a pain to figure which way it runs. There are also different EGR valves for the pre 82 engine which yours is now so the one you have isn't likely working right.
Does the ported vacuum work right? When I use my hand and snap the throttle open while watching, I can see the timing advance lever move in time with the throttle.
If you open the distributor cap, can you grab the rotor and make it move in one rotation? It should feel like it is under 'heavy' spring load and should snap back instantly when let go. If this isn't smooth, maybe someone didn't know or forgot to oil the wick that is located under the rotor in the center of the distributor shaft. This wick keeps the mechanical advance plates moving freely. I have had to remove a couple CJ distributors and take them apart to free up this plate.
Then there is the carb linkage. I have seen several over the years that had the link for the accelerator pump in the wrong hole. This also controls the vacuum piston and main jets' needles.
The engines run fine, but when you floor it, the main jets needles go in the wrong place and it bogs.
Then there is the 'Nutter' directions on tuning the carb..... I believe they are wrong and the emissions sniffer agrees with me.
I started an experiment over 3 years ago on the mix settings for the stepper motor and then got smucked up pretty bad in a car accident as a passenger and forgot about my test until really recently when I realized my top end power was gone and my mileage sucked the big one.
Nutter says to put the stepper at full rich or to have the pins all the way in, then adjust the idle mix from there. Well, this 'will' allow a good idle mix, but not a high speed mix!
Stock the pins are supposed to be centered, then the stepper adjusts them from there according to the O2 sensor and things.
I believe the pins should be left in the center and then the top speed mix will be proper once the idle mix screws are set. This is the way I have passed emissions.
I just checked the power difference and the mileage difference.
Set the 'Nutter' way, my power dies in the 3500-3800 rpm range and tops out bad going up hill. It also spits out black smoke when shifting from
3rd to 4th and the mileage is down to 13 or so. Third wouldn't top 65 mph...
I put the pins back in the center, (they can be rocked back with a mini screwdriver) reset the mix and now have a top end of 4400 rpm with 2nd gear back to 52 mph and 3rd back to 75 mph when needed to pass and my gas mileage is back up over 20 mpg.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: N>
I think the first course of action may be to ascertain the stepper motor pin settings. I think I may have moved them out one click (that is to say, when looking down the barrel, one click toward the front of the vehicle, right?) so should move them one more click. It does feel a bit like an overly rich mix issue.
I rebuilt the carb recently and am quite confident that it is assembled correctly.
How do I check the EGR's effect on performance? Just block the vacuum tube that actuates it?
I will let you know what I find.
By the way, my axle problem ultimately resulted in having the whole back end replaced. The spun bearing had at some point likely heated/warped the end of the housing keeping the seal from ever working properly. Bad news: new rear end. Good news: new rear end with 8 months of warranty.
The nutter directions will move the pins all the way into the carb. They control an air passage so all the way in shuts it off which means full rich for both the idle and the main high speed jets. Only the idle is easily adjustable.
I would guess if you had the right tools you could change the main jets size, but.... Mine goes like a scalded cat with them in the middle
I think they should be in the middle which I believe is 2 steps out from full in. If I am mistaken, it could be 3 steps. I would appreciate the feedback on yours.
I just drove my son out to a wrecker for a computer for his van and pulled into the insane 401 highway for the trip. Mine pulls fast up to
50 mph in 2nd at 4200 rpm, then 75 mph in 3rd at 38 or 3900 rpm, then
4th. I stayed with the traffic in the middle lane at 75 mph or 120 kph at 2700 rpm then went into the fast lane and tried to keep up. I hit 85 mph at 2850 rpm and pinned the needle solid at 3000 rpm. I then pulled back over into the middle lane at 75 mph because I was holding up traffic and that is illegal to do on that road.
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