Dead spot

**dbeardslee** · 10-26-2008, 09:43 PM

Ivan - I had a little bit of a flat spot below 3k. Rebuilt the carbs with a kit from carbkitscapital that included new slide needles. I also junked the squished brass floats in favor of plastic. I got rid of the filters on my vent tubes and blew them out with my air compressor (should only be done with the bowls removed). Flat spot gone, gas mileage up. I would be looking somewhere in the pilot circuit as that's what you're running off of up to 3k.

**XSPastor** · 10-26-2008, 09:58 PM

I agree with dbeardslee. It's gotta be something in the pilot circuit. Are you sure a PO didn't break the pilot screw tips off and block the jets? You're gonna have to clean those carbs and pay special attention to the pilot circuits. If the needle tips were broken off in the past, you're gonna have to get those out before this thing, er I mean lady will run right. If you're absolutely sure the carbs are right, check the ignition pickup wires. Check to make sure all the cylinders are firing at idle by checking exhaust header temps.

**prometheus578** · 10-27-2008, 05:27 AM

Don't know iff'n you're runnin' cheap pod filters... the one's with the lip that partially covers the air intake for the idle circuit.

**Ivan** · 10-27-2008, 08:46 AM

Originally posted by XSPastor

I agree with dbeardslee. It's gotta be something in the pilot circuit. Are you sure a PO didn't break the pilot screw tips off and block the jets? You're gonna have to clean those carbs and pay special attention to the pilot circuits. If the needle tips were broken off in the past, you're gonna have to get those out before this thing, er I mean lady will run right. If you're absolutely sure the carbs are right, check the ignition pickup wires. Check to make sure all the cylinders are firing at idle by checking exhaust header temps.

I think the same thing about the pilot circuit. I am sure the pilot screws weren't broke off. In my wrenching days I have rebuilt carbs numbering in the thousands. What this means is that when I rebuilt my carbs, not one part was left attached to the other. I even took the butterflies out and soaked the throttle shafts. I am pretty thorough. If you ever need a QuadraJet rebuilt, I know ALL the tricks to making them better than factory. However, this was my first shot at MC carbs.

I have checked the pickup wires, and they are fine. Also, all the holes are firing. I checked the headers with my infrared temp gun, and they are all 300º+.

Is it possible that the pilot jets need resizing? This is what my gut instinct keeps telling me, well, that and eat more steaks.

I have not been schooled on the difference between changing the fuel jet or the air jet. Even through some extensive research, I haven't seen a good explanation. Only thing I have really seen is that bigger air jets tend to make engine idle with more closed throttle, and bigger fuel jets tend to make it idle with more open throttle. I have no idea how to figure out where the correct sweet spot is. Maybe I just need to put on my tribal voodoo head dress like I did when rebuilding Holleys and Thermoquads. What I have found is that the pilot screws will not open enough to make the bike too rich. to the point of stumbling. On cages, I would adjust the idle to the point it was rich enough to stumble, then lean it until it just quit. I read somewhere on this site or another that they should be tuned just richer than a lean stumble. I have figured out this means it is too lean and makes the idle to main jet range very rough. Maybe it is still too lean.

Prom, good idea about the pod filters. I posted up pics of my install, showing how I cut the factory velocity stacks and installed the pods on them. look here. Do you think this setup could indeed be the culprit?

One other question: I out an old pilot jet in the vacuum line running to the ignition advance, since when running, the advance mechanism was bouncing around wildly, until it was at full advance. The restrictor keeps it from bouncing around likt that, but I am not sure if it is the correct way to do that.

**randy** · 10-27-2008, 09:16 AM

Originally posted by Ivan

the advance mechanism was bouncing around wildly, until it was at full advance. The restrictor keeps it from bouncing around likt that, but I am not sure if it is the correct way to do that.

An indication that you may have the vacuum line connected to the wrong nipple. The vacuum line should go to the nipple on carb #2, NOT to the intake maifold. If you've got the line on the correct nipple, the bouncing may be caused by out-of-synch carbs as one member previously posted.

Before proceeding, be sure you've got the corect nipple (always good advice

)

**dbeardslee** · 10-27-2008, 09:23 AM

Quadrajet - Now that's a carburetor! Your a man after my own heart

.

I must have been typing at the same time as Randy, and was thinking the same thing about synch. If that's not right the rest of your efforts will be for naught.

On the mixture adjustment, I always use a colortune plug to adjust mine. Some people swear by colortune, others swear at them. I use one because one turn on a given mixture screw is seldom going to provide the exact same mixture as one turn on another carb. On some of my carbs I've got 'em turned out a couple of turns, on others they're almost all the way in with the same result in the combustion chamber. I've tried doing it by ear, and by rpms with poor results, and I keep going back to colortune. My $.02

**Ivan** · 10-27-2008, 09:27 AM

Yep, it is on the right one, ported, and I have the carbs synced pretty well. She will idle slow enough I can hear the primary chain slapping around inside the engine. I don't keep it that way, but let her idle where she smooths out, which is usually about 900-1000, depending on her mood. I figured the bouncing was from it being on a single cylinder, with the pulsing vacuum.

She is as smooth as a singer sewing machine, but just gutless in the low rpms.

As far s the colortune, it would be fun to mess with one of them, but I ended up putting the throttle lock on at 2500 and tuning the pilot screws until it was nice and smooth, which ended up being anywhere from 2 - 4 turns, depending on which cylinder it was. FWIW, that is the best idle I could get as well. As of right now, the three day work week is hurting me, and we have a sick pup. "buddy" is not doing well, probably addicted to the gas fumes, since he loves helping me work on the bike.

Vets are expensive.

**egsols** · 10-27-2008, 09:29 AM

Randy beat me too it, I was wondering the same thing, whether the line is hooked to the carb, and not the intake boot. Something else I remember is a tech bulletin for the G's and H's regarding the replacement of vacuum advances to cure knocking.

**dbeardslee** · 10-27-2008, 09:35 AM

Ivan - On the SH I think the timing is fixed, but I have seen references from other owners that there is some slight adjustment that can be done. Have you checked it? I hope you meant the cam chain slapping around. A primary chain doing that would probably be a very bad thing

**Ivan** · 10-27-2008, 09:49 AM

The PO was kind enough

to hog out the holes on the timing plate to make the timing adjustable. I did put a timing light on it and lined it up with the marks on the wheel. There were three marks at the T mark which were probably too close to be much more than a degree of timing, when compared to a wheel off the 80 engine I have that has actual degrees marked on it. I also found this to be a touch too advanced, and I retarded it maybe about 2º, which makes the deceleration popping out the exhaust nearly disappear.

As far as the primary chain, maybe it isn't that, but the engine will chug along at about 400 rpm in idle, although it is not a smooth idle.

**dbeardslee** · 10-27-2008, 09:58 AM

Have you checked your compression?

**Ivan** · 10-27-2008, 11:07 AM

Yes compression is all normal and consistent, although I don't recall the numbers. It really doesn't "feel" like a compression problem.

Usually when I get stumped like this, I have to walk away for a few days, and talk to other people to get fresh ideas. This is a good thing, because I took her out this morning, and blasting around at 35ºF is neither conductive to reasoning or soothing in any way.

Maybe if I get SWMBO something nice for Christmas, she will spring for a colortune and a Morgan carb syncro.

**dbeardslee** · 10-27-2008, 01:05 PM

Ivan - It just hit me that there's another thing that could be the culprit - fuel. Did this just start or has it run across several tanks? If you run it down to reserve, or if you run vacuum petcocks in the prime postition you draw from the bottom of the tank and you can suck all kinds of nasty stuff into the fuel system. Seafoam is, among other things, a gas dryer.

Also, a number of us have been following xschop's lead and adding acetone to the gas. 1 oz per 5 gallons. It breaks the surface tension on the gas and allows it to atomize more easily. Makes a noticeable difference in power, and can also improve gas mileage. Don't excede 1 oz per 5 gallons as you hit a point of diminishing returns. The boys are even making up names for it now - gacetone (egleaves) and gas Y tone (chop). Gotta love it

**Ivan** · 10-27-2008, 03:59 PM

Nah, its been doing it for several tanks of fuel.

Not sure about the acetone. Might give it a try, but I don't think it will cure anything.

As far as crud in the tank, its possible, but the tank looks very clean with no rust and I cleaned the screens on the petcocks when I resurrected the beast. Also, my needle seats have screens on them, so no large chunks should make it to the bowls. Water is not likely the problem, because that would effect all ranges of the power band. I also pulled the pilot jets out and checked for obstructions there, and there were none.

I ordered some size 45 pilot jets today, just to see if I need more fuel in the low end.

Dead spot

Dead spot

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