fuel shutoff, replumbing, & individual filters

[TopCatGr58]

Originally posted by Mike Hart
Dunno yet, T.C. Still have to test the 115's - who knows, maybe I'll have two sets available

What is your plug color like? I would think with your airflow they should look really white after a medium-to-high rpm run...

I checked out your plug picture, and mine are no where near that tan;they're barely off white!!! But then again, I always run at Medium to High RPM, almost never let it get below 4k except when stopped! Would be interesting to try a size or two larger. I'll patiently await your finalization process!

[Mike Hart]

Then you are definitely running too lean! Not good!

Hope to try some 117.5's later today, will post.

[Robert Haller]

Suggestions I've seen for doing plug checks to check on main jets say to run at 7000 + rpm. Since I rarely rev that high, should I really be concerned with the main jets (I've got stock jets on a 79 special with 4-1 exhaust and K&N stock filter replacement)? Instead focusing on needle clip position and float height ? My engine's sweet spot is 4-5 k rpm and that's where I normally run at. Or is it all interconnected, even if I don't usually run at WOT?

[Mike Hart]

well yes it's all interconnected, the circuits overlap. The needles meter the flow from the mains. RPM isn't so much the deal as load on the engine, so my last test was mostly WOT. At WOT the needles are all the way up. But even when they are only part way up, they still depend on the mains.

Most tuners say, get the mains right first. Then you can dial in the other ranges based on the right mains. You are right, you can tweak your needles and floats, BUT, only after you have the right mains. A guy can wind up chasing his tail around doing things in the wrong order.

How's your plug color? If your mains are too small, the plugs will be whitish at any rpm range test above 3500 or 4000rpm.

I would think with the airflow you've opened up that you would need to go up on your mains, but plug color will tell you. The bike will run good lean, but it gets really hot, you can even burn pistons or valves - yikes!

[Robert Haller]

My new header pipes that I've had for at least 3k mi. have only turned slightly gold, so hopefully that is a sign I'm not too lean. But I agree I need to do a plug check. Any rpm at least 4k ok? (most suggestions I've seen say 7k).

[Mike Hart]

Got a long hill you can go up so you really load the engine? That will give the best results.

[Robert Haller]

Possibly, but not for more than a minute or two. Is that enough?

[Mike Hart]

probably - try it and report back

[xjguy]

hey mike' i think the plug looks a tad on the lean side.-by the way
i read this post for the 1st time saturday-right beore i went out to the garage to connect the tubes from the air box-started on it friday nite- but after about 20mins with the wife - i decided to have a beer and think about it. saturday by my self i realized it all slides together easier if you take the carbs out of the intake boots on the engine and install and tighten the ones to the air box 1st- or maybe i just got lucky- so i give up where do you get the mini filters? maybe i can get some in my stocking this christmas' xjguy

[Mike Hart]

or...

see this thread

[xjguy]

quick!

that was quick-thanks- xjguy

[Spotty]

Streamlineing

Good Day.

I stumbled accross your fuel delivery modification and gotta say that I like what i see. I have an 84 XJ (Canada Only) and have started to have fuel overflow problems again. After lookin at what you have there I think I will have to make some modifications to mine. I have already moded mine and eliminated the octopus....When I did my original mod I found that fuel flowed form only one side of the petcock when in ON or PRIME. The other side is only used for reserve. Since I have a fuel gage on my bike and I always turn my petcocks off when I finish riding I rarley find the need for reserve. What I did was plug the outlet that was used for reserve and run only from the main outs. The other thing that I did is run one petcock to one half of the carbs. I couldn't find a Tand Y fittings that would allow me to connect all the lines together so I just ran them from the petcock direct to the carbs bypassing the Y and T ftting's altogether. I did this about two years ago and have yet to be stranded due to a fuel flow problem. Just thought I wouold share that with you incase you want to streamline your system a little bit.

You mention in your first post that you do not have any fuel starvation problems with the lines running down as low as they do. I was often tempted to run my lines low like that myself but never got brave enuf to try it. After reading your post I think that my modifications will incorporate some of your ingenious design techniques.

Thanks for the post.....

Spotty

[Mike Hart]

Thanks for your nice remarks, Spotty.

I found RES and PRIME to be on the rear tap, and ON on the forward tap. But in any case, the Y's (got them at NAPA) eliminate any confusion in that area.

I like running both petcocks to one shutoff first, then to both the carbs, because if fuel is in only one side of the tank while you're on RES, you still get flow to all carbs. Good to hear you haven't had any fuel flow probs! There is certainly more than one way to do things, eh?

oh btw, the stock configuration had the fuel coming in from below, so Yamaha didn't think it would be a problem, and neither did I. What counts is the height of the fuel tank, the line can go all over creation, but if the carb input is lower than the tank, fuel will flow, your basic siphon... except...

Actually I'd be more concerned about a fuel line that went ABOVE the petock level!!! Now there you could get some air trapped and interrrupt flow. Below? nah, no worries

Basic siphon - keep all points between the source and the destination lower than the source. Okay, you might get away with it sometimes, but not always!

[crunchbird]

My lines are just like Spotty's, but long and looping low so that I can raise the tank to fiddle with the carbs etc. I have not had a problem, and I don't see why I should--the tank is higher than the carbs, the line could loop to the floor but gas would still flow.

Someone with this setup joined them with a Y for two reasons. First, added a filter. I would like to do this but there are teenyweeny ones and there are big car ones. Mike, what should I get?

Also, very clever, you only have to turn on one petcock. If you totally run out of gas, there is actually some gas on the other side of the hump in the tank which you can access with the other petcock. Also, only one petcock wears out, you can use the other one while you wait to fix it.

[Mike Hart]

David, I have no filter yet, still looking for the right one!

My carbs were so clean inside, I figure I have time to find what seems right.