Soon to be boat anchor, CARB PROBLEM, 1982 GS450

[GmanGS450]

I have been messing with the jetting for 3 months on this thing and its getting worse! Now I have a hug dead spot at 4-5k, I mean if you don't make it past it the bike will pop and sputter and not raise RPM even rolling the throttle to WOT. when I do get past the dead spot the bike bogs to 9k but with hardly any power. It idles great, and has alot of power to the dead spot.

I am going to try and make some velocity stacks and give that a shot, but iam about to give up and get VM's.

Current set up.
The bike is custom and the motor and carbs are from different years. I did not see a read flag in my research to say that the 1979 GS450 carb were not a bolt on to a 1982 GS450 engine. now onto the goods.

-k&N pod filters.
-41 pilot
-160 main
-mixture screw 3 turns out.
-needles shortened needle by 1mm and tapered them. "Using a drill sand paper and a caliper measuring multiple points to try and make them match"
-custom shorty exhaust with reverse cone muffler, as close to straight pipe as possible.

Please help.

Below shows the bike with the UNI-filters on it. i was trying out different things at the time.

[GelandeStrasse]

Focus on sourcing an appropriate air box. Likely that will solve your problems in the time it takes to fit it

Edit: and change all jets, needles, filter and idle screws back to stock.

Double edit: I know that's not likely what you want to hear but it'll work
Do that, ride and enjoy, THEN start fiddling with pods and jetting. Then put it back to stock because you prefer it running properly

[GmanGS450]

An Air box is not an option, it would make me cry every time I looked at it.
Is there any data on a plenum size or flow characteristics that someone has found, I would like to make something to try and fit the look of the bike if thats what i have to do.

[Guest]

cry more than sending it to the bottom of a lake?

An Air box is not an option, it would make me cry every time I looked at it.
Is there any data on a plenum size or flow characteristics that someone has found, I would like to make something to try and fit the look of the bike if thats what i have to do.

[GelandeStrasse]

it would make me cry every time i looked at it.

lol ........

[Badooka]

Why is that fuel filter on there? Don't you have one on the tank? I know what your feeling like- just overcame a 3 month issue of a wall at 5K- it was a wire short-but now it runs better than ever. Just keep at it- eventually you will nail it.

[Steve]

A couple of things got my attention.

Rather than do a bunch of separate quotes, I will just to the one, but add my comments in blue.

I have been messing with the jetting for 3 months on this thing and its getting worse! Now I have a hug dead spot at 4-5k,
RPM does not really matter, what is the throttle opening when you have this dead spot?
I mean if you don't make it past it the bike will pop and sputter and not raise RPM even rolling the throttle to WOT. when I do get past the dead spot the bike bogs to 9k but with hardly any power. It idles great, and has alot of power to the dead spot.

I am going to try and make some velocity stacks and give that a shot, but iam about to give up and get VM's.
When trying to solve a problem, there is NOTHING like throwing in some more variables.

Current set up.
The bike is custom and the motor and carbs are from different years. I did not see a read flag in my research to say that the 1979 GS450 carb were not a bolt on to a 1982 GS450 engine. now onto the goods.
Personally, I would like to know where you found a '79 450. They were released to the US market for the 1980 model year.

-k&N pod filters.
-41 pilot how did you get a 41? Stock size is a 45, and the increments are 2.5, so anything smaller would be 42.5, then 40.
-160 main are those Mikuni jets? Stock is 115. Add a few for pods, add a few for your straight pipes, you probably don't need more than 140
-mixture screw 3 turns out. probably necessary due to smaller pilot jet
-needles shortened needle by 1mm and tapered them. "Using a drill sand paper and a caliper measuring multiple points to try and make them match"
You have GOT to be kidding.
-custom shorty exhaust with reverse cone muffler, as close to straight pipe as possible. again, straight pipes

Please help.

Not wanting an airbox is a personal thing, but know that there will be some sacrifices and compromises in the process. Wanting a bit more sound is also a personal thing, but there is a difference between "more sound" and "straight pipes". Also keep in mind that you are forcing your "personal thing" on everybody that happens to be within half a mile of you. The motorcycling community is having enough problems, we don't need that kind of noise adding fuel to any arguements.

Now it's time for me to say ... "please help".

.

[GmanGS450]

Steve to answer your statements to the best of my ability.

4-5k is half throttle.

The title for the frame and the label on the frame before it was removed for powder coat said 1979 GS450. The origins are unknown before the previous owner. But I do know the front end is from a Canadian GSx model, that I purchased at a later date and fitted to the bike.

The stock pilots in my carbs were 17.5 and the main jet was a 125's. Yes they are MIkuni jets, I purchased them from a very reputable parts shop here in MN called Blue Cat motorcycles.

As for tapering the needles, it actually helped eliminate the back firing at 1/2 throttle.

" Also keep in mind that you are forcing your "personal thing" on everybody that happens to be within half a mile of you. The motorcycling community is having enough problems, we don't need that kind of noise adding fuel to any arguments. " - This comment is your personal idea of what is socialy acceptable and It does not help in this discussion. I am in no way disrupting the peace any more than a large Harley with slash pipes or a straight piped sport bike is. I was not trying to be cute or "cool" by stating as close to straight pipes as possible. I was just stating the facts. And Please you do not know me so please do not try and LABEL me as a problem for the motorcycle community. I have met many people over the years and everyone I have met is just like me, they enjoy motorcycles and they do not judge others for their tastes.

Now since that rant is over. Here is a pic of the exhaust showing it still has the 2-1 collector and 8-10 inches of pipe before the exhaust canister. I have tried to add a baffle plate inside the muffler and drill relief holes to increase flow to match the fuel. That was the first steps of the process.

I do not have any more questions, I will figure this out and report back with the findings, hopefully not falling of def ears.

[Steve]

4-5k is half throttle.

Half-throttle is the needle circuit. Could be your "custom-tapered needles".

The title for the frame and the label on the frame before it was removed for powder coat said 1979 GS450.

Wondering if maybe it was an early '80 model that was built in '79.

The stock pilots in my carbs were 17.5 and the main jet was a 125's. Yes they are MIkuni jets, I purchased them from a very reputable parts shop here in MN called Blue Cat motorcycles.

Very curious. 17.5 pilots are typical in VM carbs, but all the twins had BS carbs. My reference chart shows stock mains of 115.

As for tapering the needles, it actually helped eliminate the back firing at 1/2 throttle.

Yes, it probably helped some, I would be more concerned that they don't necessarily match each other. Yes, you measured several points, but ...

I am in no way disrupting the peace any more than a large Harley with slash pipes or a straight piped sport bike is. I was not trying to be cute or "cool" by stating as close to straight pipes as possible. I was just stating the facts.

Yes, that is my opinion, but it is not ONLY my opinion. And the fact that you are not disrupting the peace any more than a Harley or a sport bike doesn't help, either. Who said that they were acceptable? I appreciate you stating the facts, hopefully you can also respect my opinion, whether you happen to agree with it or not.

And Please you do not know me so please do not try and LABEL me as a problem for the motorcycle community. I have met many people over the years and everyone I have met is just like me, they enjoy motorcycles and they do not judge others for their tastes.

Not doing any judging here, not enough evidence yet. I, too, have met many people over the years, I wish I could say that they were all just like me. Alas, some of them insist on being different. However, the overwhelming majority of the people that I have met over the years can not stand overly-loud pipes. Some like to make a little noise now and then with a different pipe. I even have a header on my GS, but it's relatively quiet, something that I can tolerate riding for several hundred miles in a day.

Here is a pic of the exhaust showing it still has the 2-1 collector and 8-10 inches of pipe before the exhaust canister. I have tried to add a baffle plate inside the muffler and drill relief holes to increase flow to match the fuel. That was the first steps of the process.

In my opinion (and I know what that's worth to you), you are going about it the hard way. It would be easier to get the baffle to the noise level you want, then tune the carbs to match the air flow, not tune the air flow to match the carbs. If you were going to use that approach, you would have to end up with stock pipes and air box.

Good luck with your tuning.

.

[Guest]

Hey mate the fuel filter comment earlier is a good one, ditch it and see what happens.

I reckon your 160 mains are going to be way too big too. My setup is not going to be any more restrictive than yours I don't think and I'm running 145 mains... I have a feeling even they're a bit too big.

Definitely go back to stock pilots, but your bog spot is definitely the needle so I'd be putting some stock needles back in there too.

With my setup, I'm back to the stock needle position with stock needles, and have raised them with one shim and it's much better.

I have K&N pods and a free flowing custom pipe.