Hi All,

I've searched a bit, but had a question....

Presently, the carb backfires through the carb under constant acceleration, unless, I pull up a little on the enrichment button.

If I had an intake leak, would increasing enrichment mask this?

Does an intake leak show up in compression test?

Where else could I have a leak at? It seems worse under load (uphill, constant accelleration).

Is it safe to use "quick start" to check the intake seal? (as in spraying around the intake manifold to see if there's a leak?)

I'm at .74 on a stock EVO and over 2 turns out on the mix screw. It seems to want an even larger jet even though my jetting guide says the range only should go to .76. Any tips would be greatly appreciated.

GM

 

Popping in the intake indicates lean. Intake leak could make it lean. Compression test won't show an intake leak. Leak could be anywhere from the head to the carb or the hose going to the vacuum switch. Pulling the enricher up will dump more fuel in which would inefficiently mix with the air from a leak.

First make sure you have no leaks. I usually spray a little carb cleaner or WD 40 at each joint and listen for changes in the idle. After that is all fixed, then see where you are with the jets and start changing them. Don't forget that there are 3 jets in there: Idle, intermediate and main. They come into play at different points, but they all interactto some extent as well. Wide open up hill at higher RPM's is main jet territory. Idle is fairly self explanitory. Intermediate/idle come into play, say at cruising along at 3K rpm with low load and also with gentle acceleration from a stop.

I don't know what your jetting guide is, but in my experience, the jets that come with the carb in the kit specific for my Evo and the 883 were way off, as in nowhere close. Both sets were way too rich.

 

Three jets? I thoght there were only two! Time to read some more!

Have you ever seen a "flowchart" for the S&S E carbs? Like the one in the manual for the stock carb?

 

The S&S Super E madefor EVO'shas two jets, main and intermediate. First off, get the intake leak fixed. Then tune the carb and see how it runs, if it's still lacking, then you need to change the jets. You said you were running a .74, that is a mainjet, you need to change the intermediate jet and get it running good from idle up before you start screwing with the main jet. Make sure the engine is warmed up and the accelerator pump is off before setting theair/fuel mixture and idle screws. If you don't have the instructions for the carb, here is a link to it.

http://www.sscycle.com/iframes/instruction.php

You need instruction sheet 51-1012

 

I count the idle mixture circuit as a jet. I suppose it all depends on what the definition of the word "is" is. The idle mixture screw/circuit will effect the mixture from idle up until the intermediate jet circuit is taking over. So, there are three circuits that the gas flows through. Call them what you want, but they all three need to be tuned.

Yeah, you need the S&S destructions on that carb. Their "how to tune" section is pretty good. I just followed their directions.

After you fix the intake leaks, make sure the rest of the carb is in good shape. Clean out the jets, blow out the passages, etc. before you start swapping stuff out, unless the carb is new of course.

 

OK, I looked up my current jets in my bike. 1986 Evo, "Harleyized" stock exhaust (punch a 1" rod through the mufflers), S&S intake, S&S Shorty. These jets worked fine with both the stock 1986 cam, considered to be lacking as they came out with a bigger cam OEM the next year, I think, and also with the replacement Andrews EV1 cam I have in there now.

Intermediate Jet: 265
Main Jet: 64

The kit came with a 295 and 72, and it was really, really fat. I bolted it on and headed to Sturgis with it, and that was not the best move. I wound up buying hotter plugs on the road so they wouldn't foul out on me. Anyway, that 265/64 works real well on my bike.

 

Sounds like an intake leak.

I'm running a .295 int & .70 main,I believe 1 1/2 turns out, barely any accelerator pump action, with EV-27 cam. Runs great

a .74 on stock motor sounds pretty rich but may be related to your leak. Read the S&S manual, it has a lot of good tuning tips.
You didn't say what your intermediate jet size was ??

 

Thanks for the help.

Gonna check on an intake leak.

Other leaks would show in a compression check, right?

It only seems to be a problem under pressure (constant accelleration), it idles well and cranks fast.

I really love the S&S, much simpler to clean, work on, understand than the stock system. Nice to see there are plenty of others that use them as well.

GM

 

Have checked the intake twice, doesn't appear to be any leak according to the idle/WD40 spray test.

It does appear that I am running lean, as when I go up a hill it backfires into the carb, until I hit the enrichement **** a bit.

I don't think it's the igniition (crane), as it idles well and seems to run nicely at road speed, (once I kick a little enrichment in, of course)

I am running a .0295 on the intermediate and .74 on the main. Still a little over 2 turns out on the mix screw. Seems the carb is adjusted to where it should be very rich, but acts like it's lean.

What else could be producing a condition like this? Exhaust leak? Valves? Head Gaskets?

Anybody have any favorite test for these conditions?

GM

 

A compression test and a leakdown test will check your rings, valves and head gasket. Carefully putting your hand around the exhaust just after starting, before everything gets hot and feeling for air pulses, or blowing some smoke around the exhaust near the head will show a leak. Neither of those sound like your problem, though.

I think it is your carb. A 295 and a 74 sound pretty fat, but every bike is different. You got some monster motor in there or something? Anyway, make sure your air cleaner is in good shape and sealing properly. Inspect the throttle shaft bushings and make sure they aren't sloppy and sucking air. Make sure the float level is correct, as if it is too low, that will make it lean too. Make sure all the air and gas passages are clear (blow them out with compressed air). Then just start going fatter on the jets. Keep good notes. I made a spreadsheet of the jets and comments so I could see where I already was and what changes made what difference. Make sure you ride it long enough to fully warm up before judging the jets. That's over 5 miles on my bikes. You can also get a spare jet set and a drill index and just keep boring them out until they are too fat, then buy the next leaner one. The jets come in drill bit sizes, if you think about it. a 74 is a .074", if I recall. You can look up what size drill bit that is.

Get the S&S manual. It is on their web page and the tuning section is really pretty well written, as is the trouble shooting section, with lots of pics showing what passages to blow out if you're having problems.