Dead spot

[dbeardslee]

Ivan - Dropping the slide needles a notch should help on the bottom end. With the later model carbs they're a lot easier to get to.

[Ivan]

my slide needles are not adjustable.

I do have a set of older carbs with adjustable needles, I suspect could be used in these carbs, given they are not all damaged. I may try this if the pilot jets don't give any change.

[egsols]

I'm not sure how the adjustable needles would work in the BSIII's. The emulsion tubes are different and the jetting is also different. May cause even more issues. My 2 cents.

[XSPastor]

my slide needles are not adjustable

The 81 carb slide needles are adjustable. You do it by adding more washers to go one way and subtracting them to go another way. You can file the little nylon collar thinner too if one washer is too much. I have not done any of this but have read of others that have here in this group.

[XSPastor]

Hey Ivan,

Run it down for us. Intake mods, exhaust mods, any other engine mods (like the drilled-out elongated holes you mentioned in the timing plate). It just seems like you're not getting enough fuel in the pilot circuit. It sounds like you've tried all the right things. I'm racking my brain here. Any other pertinent info? Have you ruled out weak spark at low rpms? Cleaned all the electrical connections?

[Ivan]

Well, a set of bigger pilot jets and a touch of advance in the timing seems to have helped quite a bit, and my exhaust isn't popping loudly while decelerating, which is a good thing. More tuning to come....

[Ivan]

XSPastor.

I have the pod filters, I made a post about how I used the old tubes from the airbox to install them. The engine is out of an 80 standard, but I swapped the ignition stuff from the original engine (81 special). other than that everything should be stock. The guy I bought the engine I am running now swore to me that the guy he bought it from "bored and stroked" the engine. While I have never had the head off, I am fairly sure it isn't true. I haven't ever heard of anyone stroking one of these engines, which would probably entail welding the crank and regrinding it, along with fabricating new con rods. It may have a big bore kit in it, and since I have no comparison of what a stock one runs like, i could only tell by yanking the head.

Anyhoot, I put the bigger pilot jets in it, and readjusted the pilot screws, which weren't all that far off. This really helped, but there was still a noticeable dead spot, although it was only up to 2500.

Previously I had retarded the timing, to rid myself of rather embarrassing deceleration popping, which I am sure a few at the Talimena rally got an earful of. Now with the richer off idle, I have the timing advanced back to where it was when I checked it with the light. The dead spot is all but gone, still a little hesitation just off idle to about 1400. I am back to pulling the front wheel off the ground if I goose it (750 final drive and 300+ pounds of fat guy, so I think that is pretty good) and the engine seems more happy all around.

[XSPastor]

Sounds like you've pretty much got it. Good work! Did you swap the ignition boxes when you swapped the ignition parts on the engine? Still have the stock exhaust?

[Ivan]

The ignition stayed with the bike. I have the 81 ignition setup on the 80 engine. I have a TCI and an advance plate and trigger off the 80, but I I kept the 81 stuff since I didn't know at the time if the wiring harness was the same and didn't want to swap it anyway.

I think my exhaust is a MAC 4-1. Not sure, exactly, but it looks like the pics I have seen, except it is all smashed on the bottom two tubes. Amazing what a little air in the forks can do for you.

[XSPastor]

I wonder if the mixture of 80 and 81 ignition stuff is causing your flat spot. I know the 81 ignition box is different than any other year. If the curve is different, that could be causing your flat spot. Maybe one of the ignition experts will speak up...

[TopCatGr58]

Hey Pastor,

He doesn't have 80-81 parts mixed, he has the 80 engine in his 81 frame, and is using all of the 81 ignition components, the TCI, pickups, timing plate and stuff. He just has the spare 80 TCI/PLates and such left over from the swap. He was right to keep and use the 81 stuff on the 81 frame even with the 80 engine. Yes, the 81 TCI has the Cent. Adv. curve built into the TCI, that's why it only uses/has a vacuum advance/retard unit, but no mech. cent. adv. weights/components.

Ivan, I will say that both Indy filters and 4-1 pipes tend to cause a loss of the low rpm grunt, not to mention trying to accelerate these engines from IDLE and expect them to respond smoothly when you're next to lugging rpm. I also have the same intake/exhaust setup you have, and I don't even bother running below 2K rpm, and I'm only 220 lbs! Yes, these engines are torquey and fairly strong, but they aren't a V-8 or Harley either!
T.C.

[XSPastor]

Thanks for setting me straight, TopCat!

Hey Ivan, FWIW...

I did notice a bit of loss in low end torque too when I switched from the stock exhaust and airbox to a 4 to 1 and a K&N in a drilled airbox. I'd much rather have the stock exhaust but it was done - too many cracks. Keep the rpms up and you should be good. I'm almost always between 3 and 4k.