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450>500cc idling issues

  • Thread starter Thread starter Shaun6691
  • Start date Start date
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Shaun6691

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Hey guys, so I converted my gs450 to 500cc's using a gs500 jugs and pistons and now I I can't get it to idle down low. It will idle high (2200 rpm) and rev up fine with good power but if you let it idle for very long, the idle drops and then dies of you do not give it gas immediately. When the idle starts to drop off / it runs rough and once it dies, you cannot start it up without waiting several minutes due to the plugs fouling. The idle screw adjustment does nothing as far as dropping idle to where it should be. It has new coils and wires. 40 pilot jets. Carbs synced and thoroughly cleaned. Valves are adjusted. Timing set to stock.
My thoughts are that now the compression ratio is changed (not sure if its higher or lower now) that the timing needs to be adjust from stock. Thoughts? The bike is anot 82 gs450 with pods and a 2-1 exhaust. Battery charges just fine. Help!
 
What carbs have you got on there? If you have the stock 450 carbs then size 40 pilot jets are extremely oversized as stock is 17.5 from memory.

High idle can be an air leak on the intake side as well, are your rubber intake boots nice and supple?

If your plugs are fouling at idle then my guess is not an intake leak though, more likely those pilots are way too big.

As a comparison, I have my '82 450 stock engine wise but have GS500 cams and carbs on there with filtered velocity stacks and custom 2 to 1. On the GS500 carbs, I have only gone up one pilot size to 20 and it seems to be fine.

I have'nt had to worry about timing with the GS500 cams in there either so I'd be looking at fueling as your first port of call.
 
I've actually been confused about this for a while. Both the '80 and '81 carbs off a 450L that I have were outfitted with (what I'm fairly certain were the stock) 17.5 pilot jets but I've seen a lot of threads where people refer to using jets sized in their 40's. This chart off of basscliff's site shows that this is the case for some models - I would love to know why the pilot jet is so much bigger for some bikes.
 
It's the stock bs34ss carbs. Reason I went to 40 is before it had 22.5s and was starving for fuel below 2k rpm. Almost impossible to fire. 40 is the stock pilot size for the gs500s. So it seemed like a plausible move. And it's not actually jumping to 2k rpm during idle. That's just where we can set it with the idle speed screw so it'll run. I really wish there was a write up or someone that's still active with a similar setup to mine that I could talk to. Sighh, engine build problems. Lol
 
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sam000lee said:
I've actually been confused about this for a while. Both the '80 and '81 carbs off a 450L that I have were outfitted with (what I'm fairly certain were the stock) 17.5 pilot jets but I've seen a lot of threads where people refer to using jets sized in their 40's. This chart off of basscliff's site shows that this is the case for some models - I would love to know why the pilot jet is so much bigger for some bikes.
Click to expand...

I think it's because suzuki had these bikes set wayyy lean to get past the epa. I too have read of guys pushing 40 on the pilot jets
 
Ok, in that case yes 40 will be way way way too rich on the pilot on these carbs.

The 83 and onwards 450's have a completely different set of carbs with a completely different pilot jet which has a completely different numbering system. I think some of the info in BassCliff's chart is from these which are incorrect for the '80 - '82 models.

When I still had the stock carbs on, one size up on the pilot made a big difference, two sizes up started fouling plugs.

I realise you have the 500 barrels on there but even so it shouldn't require a jump of nearly twice the pilot size.

Where are your mixture screws set?

Right now I suspect there's something else at play here I'm not aware of because that much of a jump just isn't right at all.

I'm trying to remember who on here has done the 500 barrel swap and am coming up blank at the moment I'm afraid...

Another thing... how good are your carbs condition wise? With my stock carbs I was having a nightmare of a time trying to get the idle set right, get them tuned right, and kept having "hunting" I guess you'd call it at constant low throttle openings. I just could not get smooth operation at all.

In the end I found some tiny tears in the diaphragms which is one of the reasons I ended up going the GS500 carb path as the after market diaphragms from JBM Industries don't work in the stock 450 carbs and new ones are ridiculously expensive.

Might be worth having a closer inspection if you haven't done so already.
 
pete said:
Ok, in that case yes 40 will be way way way too rich on the pilot on these carbs.

The 83 and onwards 450's have a completely different set of carbs with a completely different pilot jet which has a completely different numbering system. I think some of the info in BassCliff's chart is from these which are incorrect for the '80 - '82 models.

When I still had the stock carbs on, one size up on the pilot made a big difference, two sizes up started fouling plugs.

I realise you have the 500 barrels on there but even so it shouldn't require a jump of nearly twice the pilot size.

Where are your mixture screws set?

Right now I suspect there's something else at play here I'm not aware of because that much of a jump just isn't right at all.

I'm trying to remember who on here has done the 500 barrel swap and am coming up blank at the moment I'm afraid...

Another thing... how good are your carbs condition wise? With my stock carbs I was having a nightmare of a time trying to get the idle set right, get them tuned right, and kept having "hunting" I guess you'd call it at constant low throttle openings. I just could not get smooth operation at all.

In the end I found some tiny tears in the diaphragms which is one of the reasons I ended up going the GS500 carb path as the after market diaphragms from JBM Industries don't work in the stock 450 carbs and new ones are ridiculously expensive.

Might be worth having a closer inspection if you haven't done so already.
Click to expand...

I know tkent has done the swap but he's got stock exhaust and air box. The carb condition is good but I'll take another look at the diaphrams. I was afraid of that (too big of pilot jetting)
 
Ahh... for some reason I thought Tom's was stock!

Anyway, the stock exhaust and airbox aren't really that big a change compared with pods and a 2 into 1. In fact another question I should've asked... what pods do you have on there? If they're Emgo or similar then they're absolutely horrible and regardless of any filtering issues they have a lip inside which causes big issues for the airflow going in to the carbs.

I had some crappy cheap ones when I first put the 500 carbs on mine and it was a nightmare trying to tune the carbs properly, even harder than getting the stock carbs working reasonably well with the buggered diaphragms.

I've gone to velocity stacks with a foam filter over the top, the difference is incredible. Throttle response is so much smoother and I have been able to get a much better result from tuning also, not perfect because I'm just not that good but definitely good enough.
 
Lol I've been lurking around here long enough to know about emgos. I have k&n cone pods but I've considered going to uni foam filters. Is it possible that the 22.5 pilots were too small and the 40 pilots were much too big? I'm gonna take a look at the diaphrams. I have a spare set. Last I checked they looked good.
 
Hahaha glad to hear!

It's most definitely possible 22.5 are too small and 40 much too big... in fact I would say it's more than likely to be the case.

Typically when tuning you only adjust pilot jets +/- one size at a time, maybe two if you're doing something really radical. Main jets you would do 2 sizes +/- or maybe 4 if you've got an open pipe and velocity stacks or something along those lines... at least that's how I've tried to do things after much reading around the interwebs at large and here...

Oh, the other thing I just remembered with Tom's 450 is that I believe he lives/rides at high elevation, so he needs to lean his jetting out to accommodate that if I remember correctly, so any settings he has will likely be too lean for yours.
 
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