1977 Gs400 rejetting

[KEITH KRAUSE]

I make a good crack & some wise guy has to point out the obvious.:?
I do love to ride, but the edge is taken off somewhat for me if I feel that the machine is not running as well as it could be. You know, there's that special feel to a machine when it's giving you all it can. That's what I am looking for from Gustav. He's a little bike, so maybe what I am shooting for is for him to run like a raped chimpanzee.

And that's why I try to help here. I want your bike to run its best.
Maybe my experience will help and maybe it won't, but I think each thread over and try my best.

[West]

And that's why I try to help here. I want your bike to run its best.
Maybe my experience will help and maybe it won't, but I think each thread over and try my best.

I can see that. I appreciate your help, I can see your expertise is invaluable, literally. You can't buy this kind of expert help, unless you are Jay Leno, and if you were, then you couldn't understand the answers anyway:-D. (or need to, he just turns the key & goes).

I am still waiting for the pods, OBB hasn't even got them themselves yet, much less shipped the to me. I am hoping they will get here by the end of the week.

[KEITH KRAUSE]

By the way, I'm going on vacation tomorrow AM until August 14th. So if you need help you know why I'm not replying.
Others here should help you. I hope I helped you out and I hope there will be good news when I get back.
Please let us know how she runs because this will help others down the road. We don't get too many 400 re-jets so it's important to share info/experience that comes along.

[West]

What, I am not supplying enough details?:-D

I'll continue the blow-by-blow when I get the pods. Who knows, if my ship comes in (get a job) I might even be able to spring for that 2 into 1.

Thanks, Keith.

[West]

A new question. On the GS400 there are aluminum spacers, about 9/16" thick, between the carb boots and the cylinders. In each of the spacers, there is a small dam, approx 1/4" high, along the bottom of the spacer, approx 1/8" thick , situated at the midpoint of the spacer. These dams change the profile through the spacers from a circle to a "D" shape, with the flat side down.

The intake ports in the head are circular where the spacers contact the head, as are the carbs outlets (of course).

So, basically, as far as I can tell, these little dams would do little more than add turbulence to the airflow as it passes the specers. My understanding of intake design is that you want as little turbulence as possible, pure laminar flow is the design goal.

So, why are they there? I know that D-shaped intake ports are one method used to achieve a more linear velocity profile across the ports (and therefore less velocity variation, promoting laminar flow) but these dams would hardly do that.

I have thought about grinding them down, so the spacer profile would match that of the carb outlet and the intake port, but of course hesitate to do that as the procedure would be irreversible without replacing the spacers.


Anyone care to comment?

[West]

A bit of useful info. Found some viton o-rings that should (absolutely should - caliper measured) fit the carb boots on the GS 400. The boots & O-rings do not show up on the fiche listings at bikebandit, or anywhere else that I can find. Mine are a bit flat, but are still sealing, I'll replace them next time I go in there.

http://www1.mscdirect.com/CGI/NNSRIT?PMPXNO=1797492&PMT4NO=0

Still waiting on the new pods, turns out the nice Suzuki ovals don't exist anymore. OldBikebarn refunded my money after 10 days of waiting. I had to buy some Emgo's on E-bay as plan B. Shoot.

[spots25]

Please let us know how she runs because this will help others down the road. We don't get too many 400 re-jets so it's important to share info/experience that comes along.

definately, because my GS400 is going to pods sometime early next spring :twisted:

[West]

A day of discovery. I did a lot of dumb things and a few smart things, I'll leave out some of the dumb things and recovery from them in this summary both to salve my ego and to keep the recount short(er).

I got the new Emgo pods around 2:00 PM, and damn, they are pretty much nonexistent, I could almost see through them. I mean the steel mesh and chrome are OK, but the foam is very thin and porous.

I expect them to keep out the bugs and any rocks larger than a millimeter. For those who can afford them, go with the K & N's, your engine will last longer.

I did some googling, and found no info on whether these are supposed to be run oiled or not, but since they are so porous anyway, I figgered I would oil them for that much more protection. I just sprayed them with Marvel Mystery Oil & blew off the extra with my leaf blower.

I mounted them I went for a ride, and found essentially no difference between them and my previous configuration, aside from some oil smoke at first as I sucked any extra oil out of them and into the cylinders.

That config was approx (drilled out) 119 mains, 4H11 (thinner than stock) needles, and the stock pilots.

So, I popped out the mains and drilled them out to approximately 126.5's. I also swapped the needles back to the stock 4F23's, clip in lowest position.

UGLY. The bike ran so rich I could hardly start it, and it would hardly accelerate at all because of massive missing. After a mile of running the plugs fouled to the point where I almost did not get the bike home again.


I messed with the needles, leaning out the midrange, no help.

SO, 126.5's are going to be way too rich.

Just to be sure, I epoxied the holes in the mains, and after it set, re-drilled them back out to the 119 size. Now it's back to running not-half-bad, but I have a fair amount of missing in the midrange (I experienced that before when I had BRASS 119's, so I do not attribute that to the epoxy). I have the stock needles at the leanest setting, I plan to will raise them tomorrow to see if that helps. Plugs are now running fairly clean, no carbon fouling.

The bike starts OK and idles decent, but stalls occasionally before it is fully warmed up.

Where I stand now is that I think my mains range is going to be 117.5-120-122.5, I am leaning towards 117.5-120 rather than 120-122.5, because 126.5 was horrendously rich.

I intend to up the pilot size from a 20 to a 22.5, if I can find one, most places selling them start at size 30. Yikes! Well, the pilot is not as critical as the mains, anyway. Looks like the stock needle jets will do, I will see if I like the stock or the thinner needles with a little more testing. I think it ran better before with the 119 mains and the thinner needles.

When I finish all this, you guys who are intending to rejet your '400's can send me a check.

[West]

Moved needles to richest setting. Only misses a little less.


Either going to attempt to get an intermediate size on the mains tomorrow or move to the smaller (richer) needles, or both, tomorrow.

[West]

Now I have a problem. The N151.067 pilot jets I have in my bike AND that came with the other set of carbs are sizes 20 and 17.5 respectively. They are not available anywhere that I can find (checked 20 or so places) in sizes less than 30. I need a 22.5.

These are definitely N151.067's, I have researched that thoroughly.

Can I substitute VM22/210's?

[West]

Woohoo!

Bike's running great. I re-epoxied the jets last night, and carefully honed a .060 drill bit down to .0505, which should be about a 122.5. popped 'em in, she started, ran great all through the throttle range, just an occasional miss at midrange. Moved the needles from full lean to midrange, now no missing at all, little sucker moves better than he ever did.

I betcha I gained all of a 1/2 HP, but when you only have 37 to start with, that's nothing to sneeze at.

Now I will do some plug chops & fine tune it, but as of this point, I think I have it dialed in.

[West]

Well, maybe. Bike is still running very well, starts well, idles OK (not great) accelleration is better than stock, and the power band has been expanded from 7-9K to 6600-10K.

Concerns:

Plugs are showing almost no deposits at all. Just a very light carbon dusting on the thread ring. I am seeing a few (2 or 3 per plug) very small droplets (probably aluminum) on the ground straps and the insulators.

I get a little burble at 1/4 throttle, and the air screws are at 2 1/4 turns each, indicating that the pilot is a little small. Uneven idle, and it threatens to stall, but never quite does.

The carbs are much more sensitive to needle position, I tried every one, and ended up right in the middle position. It was easy to tell the difference between them.

I am concerned that I am still running too lean.

This is all with my 122.5 (approximately) mains, 20 pilots, stock needles & needle jets.

So, I ordered two sets of mains, 125's & 127.5's, and a 22.5 pilot.
I could not get the stock pilot, the N151.067's, in a 22.5 size, so I ordered VM22/210's.

[Nessism]

I'm not sure if this will help you but I fussed around with pods on an old XS400 Yamaha and could not get it to run right for the life of me. The pods were clamped directly onto the carbs. I wound up taking the intake runner tubes that connected the carbs to the air box and chopping them off where they entered the airbox. Next, I fashioned an attachment and clamped the pods onto that. So in the end I had about a 4 inch runner between the carb and pod which smoothed the air flow into the carbs. Worked like a champ.

File this info appropriately.

[West]

I'm not sure if this will help you but I fussed around with pods on an old XS400 Yamaha and could not get it to run right for the life of me. The pods were clamped directly onto the carbs. I wound up taking the intake runner tubes that connected the carbs to the air box and chopping them off where they entered the airbox. Next, I fashioned an attachment and clamped the pods onto that. So in the end I had about a 4 inch runner between the carb and pod which smoothed the air flow into the carbs. Worked like a champ.

File this info appropriately.

Cool. Thanks. So far I am pretty optimistic, It's going well, but i'll keep your suggestion in mind. Unfortunately, I only have about 1/2" from the end of the pods to the battery on one side and the old air filter box on the other. The air filter box is the mount platform for the electrical system, so that's not coming off. Neither is the battery.:-D

[West]

The uneven idling and the burble at 1/4 throttle was due to a bad plug. Replaced both, all gone.