1981 GS450E right cylinder not firing at low rpm

[prefect]

I am really starting to lose patience with my bike.

The problems began about a month ago when I decided to change the carbs on my bike. The PO put pods on and rejetted. The bike ran great, but I was only getting 28-29 mpg, which is WAY too low for a 450. I didn't have the stock air box, so I purchased the airbox and carbs from a fellow board member.

I put them on without cleaning them and without putting the large O-ring on the engine side of the carbs. It was running poorly. Lots of popping and backfiring, and it became pretty cold blooded (i.e. wouldn't start without the choke and needed to keep it choked for the first 5 minutes or so it was running) where it wasn't at all before. The right cylinder wasn't firing at low rpm either, unless the choke was on. I thought the carbs just needed some cleaning and I had an intake leak.

So, I pulled the carbs and gave them a decent cleaning (didn't dip parts, but blew out every passage with carb cleaner). I put the O-rings back on the engine side. This seemed to do no good. The right cylinder still won't fire at low rpm when cold without the choke on. It's getting great spark, but seems not to be getting any gas. I am stilling getting popping and backfiring at higher rpm, although not as bad as before. Until the bike gets completely warm (after about 10 minutes of riding), the bike won't accelerate until it hits 3500 rpm. It also bogs at full thottle at first when it's cold. I pull the throttle wide open, it hesitates for about 2-3 seconds then the rpm goes way up. Also, when the bike is warm, the rpm go back to idle very slowly, and the idle usually gets higher the longer i ride the bike.

So, in summary, I put new plugs, cleaned the carbs, reattached the stock airbox (didn't really check it for air leaks, didn't know if that could cause problems), and the bike still runs like crap. The intake boots look great without any cracks or holes. I didn't sync the carbs (was unsure how), nor did I touch the air screws (at least I think that little brass screw in the recess on the side of each carb facing out is the air screw).

Any advice would be GREATLY appreciated. [-o<

[Dan Ruddock]

Is the dead cylinder problem at part throttle and does the problem go away when more throttle is used? If yes the pilot circuit is plugged find out why, you might have to pull out fuel and air screws to make sure there is no foreign material in there. Dan

[nabrams]

Airbox leaks, air filter and boots from airbox to carbs are absolutely critical.
You slow wind-down to idle is almost certainly an air leak somewhere.
All this has been discussed many times - do a search.

[Nessism]

Those were my carbs so I feel compelled to chime in here. They were working great on my bike, just before it was wrecked, and were cleaned less than 200 miles before they came your way. My bike was cold blooded so it doesn't surprise me that they are the same on yours - 450's are famous for this. The fact that your cleaning them did not do any good is a good indication that they are clean already.

Just curious but what kind of exhaust do you have? The carbs are lean to begin with so if you have a header, you are going to have to rejet. One thing to try is to remove the air screws and look at the O-rings, maybe they have cracked since they dried out?

Good luck.

Ed

[prefect]

Those were my carbs so I feel compelled to chime in here. They were working great on my bike, just before it was wrecked, and were cleaned less than 200 miles before they came your way. My bike was cold blooded so it doesn't surprise me that they are the same on yours - 450's are famous for this. The fact that your cleaning them did not do any good is a good indication that they are clean already.

Just curious but what kind of exhaust do you have? The carbs are lean to begin with so if you have a header, you are going to have to rejet. One thing to try is to remove the air screws and look at the O-rings, maybe they have cracked since they dried out?

Good luck.

Ed

I don't doubt that they were clean when you sent them to me, but I did let them sit for more than a month before I got around to putting them on. I thought maybe they could have gunked up in the mean time.

Anyway, I'm running the stock exhaust. There might be a leak in the exhaust , but i'm not sure. I just can't figure why I have a dead cylinder at idle without the choke and i have such a bad flat spot in acceleration between 1000 and 3500 rpm. At about half throttle, it's a little surgy too.

I'll take a look at the air screws this evening.

p.s. do you have the flasher relay? Mine decided to die last week.

[Nessism]

p.s. do you have the flasher relay? Mine decided to die last week.

Hate to tell you this...but I just dumped a bunch of stuff in the trash last week - including that relay.

I just posted a thread in the For Sale forum for the last of my parts. Dumped most of the engine in the trash today since no one seems to need one. Damn shame...

Regarding the matter at hand, please let me know how things go since I feel somewhat responsable having sold you the carbs and all. I don't know what to suggest other than making sure your ignition is okay and making sure all the possible air leaks are sealed.

Good luck.

Ed

[prefect]

well, i didn't look at/adjust the air screws last night (because I was hungry when I got home and became incredibly lazy after I ate).

I was wondering, however, is there a way I could improve the seal between the airbox and the carbs? The rubber around the outlets of airbox is kind of deteriorated. Any ideas for improving this seal?

THanks,

-charles

[nabrams]

All bets are definitely off until you get all boots sealing PERFECTLY. Then there's the various other leak possibilities (see my other posts).
ALSO, poor/erratic idle is very commonly due to low compression, which in turn, is commonly due to improper valve adjustment (not enough clearance between cam and valve).
Have you actually verified compression? If not, you're just playing guessing games.

[prefect]

I actually haven't verified compression, but the bike was running prefectly aside from the low MPG with the previous carb setup. Since the change in behavior of the bike came only after I changed the carb setup, I assume that the carbs/intake/airbox is where my problem lies.

I would like to check valve clearances, but I've never done it before, and, to be honest, am a little nervous about doing it. I have a clymer manual, but i'm not really impressed by its descriptions and walk-throughs...

-charles

[nabrams]

Your old carb set-up may have been compensating for poor compression by providing an ultra-rich mixture (thus your terrible gas mileage). The valve clearance check is only necessary if the compression is low. Checking compression is easy and the guage is about $40 at your local AutoZone or Pep Boys. Now, if it IS low, you will have to at least check the valve clearance. You won't learn if you won't try. Low compression can also be due to bad rings, but this is much less common and the bike would be smoking copiously even after fully warmed.

[prefect]

i'll dive in and check the valves if i have to...

Anyhow, where can I get new boots for the airbox-to-carb connections?

-charles

[nabrams]

Someone may be selling them here (in the "Wanted/For Sale" section), or on eBay, or the dealer.
You can probably get the whole set-up (airbox, boots) on eBay for a few dollars with enough patience.
Use silicone to seal things up temporarily for testing purposes.

[prefect]

Someone may be selling them here (in the "Wanted/For Sale" section), or on eBay, or the dealer.
You can probably get the whole set-up (airbox, boots) on eBay for a few dollars with enough patience.
Use silicone to seal things up temporarily for testing purposes.

I DO NOT want to take out that airbox and put a new one in EVER again!!! :-D

Man, it was SUCH a pain the last time. I'll buy a whole airbox if I have too just to get the boots off, but I hope I don't have to go through putting one in again!

-charles

[prefect]

Well, I checked the compression, and I'm getting about 145 in both cylinders. I may check the valves anyway, because I am getting a decent amount of vibration, especially above 4k rpm.

I ordered brand new boots (engine side and airbox side) and a new petcock with all the hoses (my current one doesn't shut off at all, and the PO put an inline shut-off valve on... works ok, but i would rather have a working petcock).

The insulators on both plugs are white, which indicates a lean condition, right?

I'm sending the tins and side covers out for paint. So, in the mean time, I will dig back into my carbs and try to get the pilot circuits all cleaned out (i'll take out the mixture screws this time). I'll take a look at the airbox to check for cracks too. Is there anything else I should check?

I would really appreciate someone pointing me toward a tutorial on checking the valves and adjusting them. THANKS!

-charles

[prefect]

another thing...

Can you really add a MAC 2 into 1 exhaust on a 450 without needing to rejet? I wouldn't do it until I have everything ironed out in its stock form, but I was thinking about adding one in the future.

-charles