Did I break it again? Popping after cleaning.

[Guest]

I recently fixed a couple of oil leaks, some of which had been trickling for a while, so I did a bunch of cleaning while I had the bike apart. I had quite a bit of oil on the outside of the airbox, so I cleaned it with simple green.

I had some popping at around 4000 rpm after I got everything back together. It got better after the first ride, but I can still hear it once in a while even after the bike's warmed up.

From reading around GSR I think popping usually indicates a lean mix, so I was wondering two things...
1.) Could I have messed with the air filter if some Simple Green got in the air box? You know, might it have cleaned off some of the required oil?
2.) I had some difficulty getting the airbox boots to mate correctly on reassembly. I think they're sealed, but how much of a factor might that be?

[chuckycheese]

Simple Green

I don't think the Simple Green has anything to do with it. If it didn't backfire before, you've got to figure you're sucking in excess air. Check youe connections again and make sure they're correct and tight. The air draw is critical on these 'beasts'.

[Roostabunny]

I don't think the Simple Green has anything to do with it. If it didn't backfire before, you've got to figure you're sucking in excess air. Check youe connections again and make sure they're correct and tight. The air draw is critical on these 'beasts'.

OK - I think I'm getting it. So they really engineer the heck out of that air flow, and if anything changes the amount of vacuum (e.g. leaking airbox connection, under/over-oiled filter) the it'll change the mixture. I know this is basic stuff, but I'm a total newb wrench.

So, carb boot leaks or bad intake o-rings are even more critical because they're actually after the mixture is produced and have a comparatively huge impact. To put it another way, an air leak before the carbs will lean the mixture some, and an air leak after carbs will lean it out a lot?

Like you said, I guess first steps will be to make sure my airbox boots have the seal they need, then double-check the filter. I replaced the intake o-rings when I had the carbs off to rebuild the cam chain tensioner while fixing all those oil leaks.

[tomm]

In the process of bringing my 78 GS750 back from the grave, I found the two things that made the most difference to getting it to run right where replacing the carb boots (engine side) and o-rings, and then sealing the end caps on the air box (I had already replaced the carb boots on the airbox side). This was after everything else, like carb cleaning, valve adjustments, carb sync, etc had already been done. Could not believe how much a difference sealing the end caps on the airbox made, especially above 1/2 throttle under load. So yes, properly controlled airflow is critical.

[Roostabunny]

In the process of bringing my 78 GS750 back from the grave, I found the two things that made the most difference to getting it to run right where replacing the carb boots (engine side) and o-rings, and then sealing the end caps on the air box (I had already replaced the carb boots on the airbox side). This was after everything else, like carb cleaning, valve adjustments, carb sync, etc had already been done. Could not believe how much a difference sealing the end caps on the airbox made, especially above 1/2 throttle under load. So yes, properly controlled airflow is critical.

You know, I might have a quick fix in the airbox cover seals. I had difficulty getting them to line up right, didn't realize how important they were, and settled for a good "squish" rather than checking for a complete seal. Could be I've got a gap right there. Dare to dream it's that easy!

Next suspect is the airbox boots, which is tougher. I worked at it, but might still be able to get them on there better.

What about the boot connection to the airbox? Now that I think about it, one of those boots came loose from the airbox a lot easier than I expected. Could it be that they're shrunken a little and letting in air up there?

If so, how long can I wait on those boots if they are the problem? The popping's not too bad, but his bike is my work commute, so I can't risk damaging it. The $40 for new airbox boots was planned for Feb after I replace the fuel petcock (lost vacuum) for around the same money in Jan.

[tomm]

I found that the airbox end caps had a bigger affect than the boots between the airbox and carbs, although mine were still in pretty good shape when I swapped them out. Also hard to really judge, since I swapped the engine side boots at the same time. But bottom line is that those two changes kept the idle from hanging and stabilized it. Prior to that, it just wouldn't sync, and I couldn't get a consistent idle.

I thought I had the end caps sealed pretty well too. The rubber gaskets were still in place and soft and I figured that should be fine. But I just couldn't get it to run strong above 60 or 70 mph, and #3 consistently ran lean no matter what I did. Kept reading though in various threads about the sensitivity to air flow, and I think a reply by chef1366 finally tweaked me to try sealing them. I used silicone sealant, and it was like a different bike. A little fine tuning on the pilot circuit after that was all that was needed.

[bwringer]

2.) I had some difficulty getting the airbox boots to mate correctly on reassembly. I think they're sealed, but how much of a factor might that be?

This could be a huge factor... none of the GS models (with the original airbox, anyway) will run right if the airbox/carb boots are not PERFECTLY seated.

This can be a monumental struggle -- these boots get hard and shrink over the years.

Sometimes, the airbox gets bowed in bit in the middle so the boots don't seat correctly on the two inner carbs. Of course, these connections are nearly impossible to see clearly. I've had to improvise a pushing stick to apply pressure to the middle of the airbox.

I think you mentioned further down that you had budgeted for airbox/carb boots next month. Might want to move that up... new boots make this struggle easy.

In the meantime, pop the airbox off and start over.

[Roostabunny]

I think you mentioned further down that you had budgeted for airbox/carb boots next month. Might want to move that up... new boots make this struggle easy.

In the meantime, pop the airbox off and start over.

Alright, well I'll have a do-over on assembly and see how it goes. Meantime, this fiche seems to indicate there's left and right ride boots. Maybe I got 'em turned wrong?

When I do order, am I reading this correctly? I'll need two #11's and two #12's?

Pushing stick might be handy. Silicone spray? WD40? Any other tips for getting those suckers on and then keeping them from squirting off when I tighten the clamp?

[Roostabunny]

Check these out - hopefully the pics are clear enough to get a view. They're both from the left side of the bike looking up toward the airbox. The first one shows the connections (not too proud of those at the moment) and the second one tries to show a gap between the boot flange and the airbox hole. Looks pretty shrunken to me.

[Roostabunny]

Pic #2 attached

[Roostabunny]

How the Sam Hill did I become a Senior Member? :shock: It's not time or experience. Gotta be the sheer number of posts.

Too bad work promotions don't work that way. :-D

[salty_monk]

Yep that'll be the culprit... Well worth getting some new boots. I just did & my originals were actually pretty good but it's still better!!

[Casino Joe]

Has anyone ever tried using lenths of radiator hose to replace the airbox tubes? $50 for four rubber tubes is a little hard to justify.
I'm thinking a length of rad hose that fits over the carb inlet should be a tight fit in the airbox opening and provide a pretty good seal.


Sent from my iPhone

[Roostabunny]

Has anyone ever tried using lenths of radiator hose to replace the airbox tubes? $50 for four rubber tubes is a little hard to justify.
I'm thinking a length of rad hose that fits over the carb inlet should be a tight fit in the airbox opening and provide a pretty good seal.


Sent from my iPhone

Can't disagree about the price being a bummer. I did check Flatout, MrCycles, and BikeBandit and found that Flatout had the best price (part + shipping) of $40.90. Next best total was about $5 more.

Not that $10 worth of radiator hose at the local auto part emporium wouldn't be better in terms of price.

As an aside, the fuel petcock on Flatout was about $10 cheaper than the other two.

[Roostabunny]

I think you mentioned further down that you had budgeted for airbox/carb boots next month. Might want to move that up... new boots make this struggle easy.

In the meantime, pop the airbox off and start over.

I'm game, but will I be OK with my old fuel petcock for another month? It lost vacuum before I bought the bike. Hasn't caused a problem yet aside from the obvious annoyance when I take the tank off to work on the bike.