gl1100 exhaust conversion - jetting implications?

[toomanybikes]

I'm thinking about switching the Jardin exhaust on my '81 GL1100 for a combination of GL1000 headers and HD exhaust bolted on. The potential system will not have a crossover pipe, will that cause any performance issues or need re-jetting?

I currently have the stock jetting with the Jardine exhaust and it's running fine.

[desertrefugee]

I would not expect any need to consider re-jetting for this exhaust swap. Intake changes wreak havoc with factory jetting, however.

[Whiskerfish]

I am not an exhaust expert but as I understand it the crossover does contribute to slightly improved torque. But no there should not be any "need" for jetting changes.

[Fred Camper]

Most of us who eliminated the cross over did not do any jetting change and did not notice any issue.

[redglbx]

No rejetting needed, but if it were me I would use MAC replacement head pipes since they actually use a collector for joining the 2 head pipes vs the terrible oe pipes the just run the back (cyl’s 3 &4) into the front pipes at nearly a 90deg angle, just terrible ! Probably doesn’t make squat difference but I “think” it does.

[toomanybikes]

thanks all. The headers I'm looking at appear to be factory parts from the later years of the GL1000 since the ends are slightly upswept.

There's nothing wrong with my current jardin system, but I like the looks of the HD better and the over condition would be better. Trying to decide if that's worth the $'s

[redglbx]

One other thing I would recommend is if the head pipes haven’t been chromed and are the oe black paint is to take them someplace and have them ceramic coated inside & out. Particularly if they are new parts, they’ll last forever if you do and won’t rust. Highly recommended!

[toomanybikes]

One other thing I would recommend is if the head pipes haven’t been chromed and are the oe black paint is to take them someplace and have them ceramic coated inside & out. Particularly if they are new parts, they’ll last forever if you do and won’t rust. Highly recommended!

From the ad they are def black and appear to be oe, possibly un-mounted.

How much does ceramic coating typically cost? Is DIY possible?

[toomanybikes]

FYI - here are the headers, which look to be OEM and possibly never mounted. Can't tell if they've been re-painted or already ceramic coated since I don't have experience with a finished product.

PXL_20220416_153734260.jpg (227.74 KiB) Viewed 753 times

[redglbx]

Those may be oe 1100 headers, not nearly as bad as the oe 1000 headers which have no real collector to merge the 2 pipes, as I said these are much better but the MAC headers have a true collector and are what I would use.

I believe those are just painted but of course I can’t really tell from a picture, are they coated/painted inside as well ? That’s pretty much how they do ceramic so they don’t rust and they run much much cooler than just painted do. Cost ? The last time I had a full system done it cost me $150 I believe but that has been quite a few years ago, but nothing is rusted either in 20 or so years, highly recommended !

One thing I would add is that if you have removable low speed jets in your carbs which I believe the 81’s are press’d in I would change the stock slow jets to #38-40’s from the oe #35’s and reduce the main jets from the oe 145’s to 140’s it’ll give you a much more linear fuel curve, but if the slow jets are press’d in I’d still replace the 145’s with 140’s but I’d leave the slow/low speed jets alone,,,,, my .02

[toomanybikes]

thanks, I can't tell if the insides have been painted, coated, or nothing. Not sure if I want to drop what is likely $200-$250 on coating.

My 'wing is an '81 with the original press in jets, so those are staying put. I know the *can* come out, but I've already done the full carb service without taking them out (yes, I was able to get the passages and jets fully clean), so I'm not going to change now.

probably keep the mains as is as well since I'd rather ride it for a while than preemptively pull the carbs for a relatively minor change.

[Whiskerfish]

Those look like 78/79 headers with the chrome shield removed and then PC'd/ painted.

[Jonesz]

+1 on Whiskers post.Don't know how anal you are but I have a 78. First go around I thoroughly cleaned (wire wheel etc.) and then applied HT primer, 3 coats and oven cured then three coats of High Temp flat black paint followed by oven curing at recommended temps. Could not get the headers to stop flaking paint. This though they were never subjected to pressure washer etc and used very sparingly for the first season. Looked terrible after one summer.
The next winter had them powder coated by a reputable firm and they came through last summer without any damage whatsoever. I know it is hard to justify the price of PC coating but I am happy that I had them done as I didn't want to have to paint/touch up every year. Not cheap at $180 Cdn/ about $135 US but well worth it IMHO.
Someone else might ring in on fitment of 1000 headers on an 1100. Seems to me I read somewhere that the 1000 headers have a bit less clearance but am sure that others have tried to do exactly what you are thinking.

[toomanybikes]

One thing I would add is that if you have removable low speed jets in your carbs which I believe the 81’s are press’d in I would change the stock slow jets to #38-40’s from the oe #35’s and reduce the main jets from the oe 145’s to 140’s it’ll give you a much more linear fuel curve, but if the slow jets are press’d in I’d still replace the 145’s with 140’s but I’d leave the slow/low speed jets alone,,,,, my .02

Getting back to this as I make my winter maintenance list. After several rides (not a lot due to multi-bike syndrome). there is a definite stutter then jump around 2500 rpm. This isn't a big deal since the riding sweet spot is about 3k rpm.

During the resurrection I kept all the jets as is so I assume the hesitation is the oe #35's jumping up to the 145's, unless some PO messed with the main jets.

If I don't want to pull the carbs off again, is it possible to compensate a little by backing out the mixture screws, effectively letting more fuel/air into the carb during the idling range before the main jets kick in? I currently have them set at ~1.5 turns out?

[redglbx]

Set the idle mix screws to 3 turns out and just forget about them, this may fix your transitional stutter, if not then you can add a .003in-.010in shim (not a too thick washer) under the slide needle, start with the thinnest and go up until the stutter is gone. This is a timing issue transitioning from the idle/intermediate circuit to the main circuit, so small adjustments are needed. The 3 turns out idle mixture screws will probably fix it though. My .02

FYI, At 2200-2500rpm that is the transition point from the idle circuit to the main circuit, the vacuum slides pulling the needles out of the main jets. So adding more low speed fuel through the idle screws may do the job or adding the small shims under the needles will start the mains flow a bit sooner. Just be conservative ! I learned from my time on my friend’s dyno that all Keihin carbs are just “pig” rich on the main circuit, way to much fuel. Which is why I recommended the switch from the stock #145 main jets to #140’s which provide a much cleaner jetting w/o being lean.

Every Keihin carb equipped bike I seen on that dyno (including Harley’s) all ran super lean on the idle/intermediate circuit and then went pig rich once the slides started to lift, keep in mind that the fuel is cumulative which means that each circuit just adds more fuel to the already running circuits.

Typically all Keihin carbs ran 15-15.8 to 1 air/fuel ratio on the idle/intermediate circuit (very lean)and once the slides opened the mains it would be in the 10-10.5 to 1 a/f ratio, maybe even into the high 9-1 ratio, just way to rich. So typically a Keihin carb needs a little enriching in the idle/intermediate circuit, although I prefer to leave the #35 idle jets alone and add (small amounts) through the intermediate circuit, they run cleaner and then reduce the main circuit because it just dumps way too much fuel. Hope this helps