Thanks Dr. Hess,

I have stock displacement on an '85 EVO with a Crane Hi-4 ignition, Andrews EV27 cam and stock pipes. This weekend, I broke down and bought a timing light, checked initial timing and started tweaking the timing advance. Interestingly, I got it to where it only bogs down in a mid RPM range. Get up to higher RPM's and it runs like a scalded dog. I'm now wondering if it's something in the way the ignition transitions to advance. I don't have a VOES so I am in "race mode" on the timing advance. Rotating the "advance timing" forward seems to help. But I am still "figuring" on setting that advance timing. The paper work says "rotate the unit" but that would seem to change the timing at idle and I'm not sure how you would adjust that out. Oh well, any thoughts are appreciated.

GM

 

Bogging down in mid range is probably too big of an intermediate jet. Try one smaller and see if there is an improvement.

I dunno about your ignition. I have a Screaming Eagle on mine.

 

Hmmm, did I mention it popped through the carb in the mid-range? I thought that was a sign of being too lean. Also, when I engage the "enrichment" setting on the carb, this problem doesn't happen.

I'm beginning to think I'm chasing symptoms, but haven't found the problem yet.

May thanks

GM

 

Bogs down and popping are different. If it's popping, then you probably need to go fatter. It's really a matter of trial and error. Just keep good notes. You have to pull the float bowl off to get to the intermediate, so that's a good time to blow out all the passages like the destructions say.

The good thing about EFI, well, MegaSquirt EFI anyway, is that you can log the oxygen sensor (and everything else) while your riding around and you know exactly (sort of) what's going on, then just clicky-clicky and you "changed your jets."

 

Correct me if I'm wrong, but didn't this bike set for a while without running? If so, I would take the carb completely apart, get a one gallon can of carb cleaner w/ the basket inside (any auto parts store), soak all the parts overnight (don't put anything rubber or plastic in there), wipe it all down, blow out the passages with compressed air, and put it back together with all new gaskets. Set the float bowl heigth while you have it apart and off the bike. See if that makes a difference before you start to jet it, otherwise you are wasting your time trying to get it to run right with jets. I still think your main jet is way too big, but I'm not an expert, if it were me I would start with a .72 and then tune the intermediate circuit, then come back to a bigger main if needed. If all else fails, use a BFH. (big f'n hammer)

 

Dr,

I changed out the intermediate jet yesterday. Now I have .031 and .74, which does seem a bit ritch as I can only get about 3/4 turn on the enrichment screw. When I open it up, it runs like a scalded dog, but stutters a little on the low rpm range now. Not back firing, just a very subtle stumble. I hadn't checked the plugs yet, gonna put some miles on it with this setting first, though, judging by you advice, I will probably be jetting down a bit before all is said and done.

After pulling the .0295 and eyeballing it, I think there may be some gunk in it as it is substantially different that the .031. The up side is, at least I know I'm heading in the right direction. Putting a new cam, ignition and carb on, all at the same time, has been an interesting experience. When you ad to the fact that this is a 22 year old bike (prone to other issues) I am very pleased that I have gotten to run this well.

Frankly, I'll ride it around this next weekend (Thunder Beach in Panama City Beach, Fl - THE Redneck Riviera!) as it's been off the road for the last 5 years. Sure feels good to have it running again and to know what to do to tune it out the rest of the way.

Thanks Dr Hess, for you assistance. Your input was VERY helpful!

GM

 

Anyone ever seen a "flow chart" for one of these carbs? Kinda like the way they show the mikuni in the HD shop manuals? Show the path at idle, show the path at 3k rpm?

Would love to see the actual path of the gas. Always wondered about how all them orifices connected.

GM

 

Did you get the instruction PDF off their web page?

 

Hi Dr.

I have that sheet from the web site. It's been helpful, but I still wonder about the "flow chart". Guess that's one of their "trade secret" things? Anyway, LOVE this carb. Much easier to work on than any other I've dealt with. Still tweaking in the jets. Yeah, it's slow, but I'm not gonna pay friggin' hundreds of dollars for a dyno run when I can figure it out with some riding. Guy at the dyno says, "man I can figure it out in an hours, it's gonna take you three hours of riding to do the same thing!". I think, "why would I trade in all that riding, tweaking, understanding for the chance to pay someone else my long green". Guess I'm just sick that way.

Thanks again, Dr H, your info is always right on time!

Time to ride!

GM

 

NP, GM. I just try to help out others in areas that I have knowledge and experience.

Yeah, a dyno run would be nice, but dyno time costs bucks. I've megasquirted 3 vehicles now: 20 valve 4AGE Corolla, 22R Truck and the 883. I have not dyno'ed any of them and I've tuned them all with a narrow band oxygen sensor. Sure, a dyno run would make it easier, especially on the Sportster where I have to log the rides with a pentop in a backpack, but why spend big bucks if you don't have to? And,change something and you're back to square one. Much better to know how to do it by yourself.

That S&S shorty is a good carb for HD's. I like it.Back inshovelhead days, I had pretty good luck with a Lectron also. It didn't look like it could do anything but hang on, butyou couldn't get much simpler.