GT550 J/K carb needle jet

[jabcb]

Forgot to mention the JNs — will use NOS 5DH21.

[Vintageman]

I hope they are nice inside, where the metering is done since i steered you to them.

[CAFE380]

great info in here guys , thanks ..

Hey JABCB where did you find the NOS 5DH21 jet needles and are they -3 's ?

[jabcb]

I got the last two jet needles they had, otherwise I would have purchased 3.

The “-3” refers to the clip position.
So 5DH21-3 is a 5DH21 with the clip in the middle position.

[CAFE380]

the “-3” refers to the clip position.
So 5DH21-3 is a 5DH21 with the clip in the middle posi


Wow thanks lol , that explains a few things ..

[GTandcbr]

Very interesting topic this. I have a 550j stock pipes and airbox and have been having problems with pinging on long steep hills. I have solved it by going from 27.5 pilots to next size up 30's problem is as mentioned on a previous post its a bit sluggish in town riding. Am thinking of going back to the 27.5 and perhaps lowering needle clips from three to two. See what happens

[Vintageman]

Very interesting topic this. I have a 550j stock pipes and airbox and have been having problems with pinging on long steep hills. I have solved it by going from 27.5 pilots to next size up 30's problem is as mentioned on a previous post its a bit sluggish in town riding. Am thinking of going back to the 27.5 and perhaps lowering needle clips from three to two. See what happens

I think they call it going from clip pos 3 to clip pos 4 to make it one step richer. It may fix your pinging but I suspect you miles (km) per fuel usage will be impacted... hopefully not a lot.

Did you ever look into the barrel of your needle jets to see if they are OK (perfect) inside?

[GTandcbr]

Hi, the needle jets are 12 months old as are all the carb internals. Carb bodies are ultrasonic cleaned. The bike ran fine except on long hills, I used to back off the throttle when it happened and pinging would stop. Annoying though. Thanks for the input

[ConnerVT]

Enriching the fuel mixture is really the third, and least effective, method for dealing with occasional pinging (pre-detonation).

The best thing to do is use better gas. These 1970's motorcycles were designed to burn gasoline of higher octane with lead, not the lead-free, chemical additive, and alcohol diluted stuff that is sold now. The higher the octane, the less likely the fuel mixture will detonate before the spark plug fires.

Next is to retard your ignition timing a couple of degrees. This may take a hair of power from your off throttle performance (as these bikes don't have any timing advance mechanism), but you likely won't see any difference from half throttle on (where you spend the majority of your time). This will help lower your cylinder temperature, which in turn, keeps the motor from reaching the conditions where pre-detonation will occur during the high load/hard acceleration.

Last, enriching your fuel mixture. The extra fuel does have a minimal cooling effect for the cylinder. But you also will run rich in most all riding conditions, with the engine making less power, as well as consuming more fuel.

http://www.klemmvintage.com/91oct.htm

[GTandcbr]

Thanks for those links very interesting reading. Just wish we could still get leaded fuel! Incidently I use the best pump petrol I can get here but of course it will still have some ethanol etc in it.

[GTandcbr]

Okay so I have done all three of the above so will see what happens. Petrol is 98 octane,have advanced the timing a little and have kept 30 pilots. Will test ride tomorrow.

[Vintageman]

Enriching the fuel mixture is really the third, and least effective, method for dealing with occasional pinging (pre-detonation).

ConnerVt,

Was a bit sick of working so I thought I would reply my 2 cents/experience

When you are jetted wrong, too lean for example you are just that- too lean: and thus root cause of your issues. That must be fixed first and foremost. Some times it is only at certain throttle positions: that can be the challenge Don't confuse that with over enriching, sometimes that becomes an accident of trying to get jetting correct. Stock engine, pinging Most of the time you are not jetted correctly (e.g. needle jet pitted) and again must be fixed first. Or when is the last time you de-coked your engine, carbon build up does this too.

Backing off timing on a stock engine to fix pinging to me is wrong. It may work but you effectively reduced your engines displacement, power stroke degrees. This kills midrange driving, fuel economy... mainly what you do/need on the street.

If you run too high compression you need higher octane fuel. I hate the fact most gas station share the same pump hose be it supplying low octane or high... if the person before you used low octane you select high you may get a quite a bit of low octane.. Chambers can boost you compression at certain rpms... but now we are not stock anymore

[GTandcbr]

I am due a decoke as the head and barrels haven't been off for about 15000 miles, I am about to do this, I just wonder how carbon build up would cause pinging?

[tz375]

Carbon build up increases the effective compression ratio and that can lead to detonation. It also acts as an insulating barrier which reduces heat removal and results in higher combustion chamber temperatures and it can also lead to pre-ignition if carbon is glowing red hot.

[ConnerVT]

I've just finished four 12 hour shifts at work, so just now have time to reply. Vintageman and I are going to agree that we will always disagree on some things, and we will likely never convert the other to the way we think. But it benefits everyone to put our ideas out here, so everyone can read, learn, and make their own ideas.

Detonation, pre-ignition, pinging. All different terms for the same condition - a fuel charge in the cylinder firing before intended, before the spark plug fires. Earlier, I offered three things that one can do to help reduce this from happening, which can be done fairly easily in the garage. That isn't the only, or even the best, things to help the problem.

Detonation will occur if it is hot enough in the cylinder for fuel to combust before intended. Poor cooling, residual fuel, or hot spots acting as a glow plug all will contribute. One of the main reasons we see detonation in these Suzuki motors is that the combustion chamber is poorly designed. No one was designing engines the way they do today, for maximum fuel mileage (US CAFE laws) or to reduce emissions. Much learning has taken place since the 1960's.

The Suzuki cylinder head is not the best design. It has way too much open area for optimal, even cooling, and does not scavenge the spent fuel very well, or burn the fuel as completely as it could. One of the best things to reduce detonation is to replace the cylinder heads with those having a good squish design. This improves both cooling and exhaust scavenging.

Discussed here may times is the poor fitment of Suzuki's head gaskets. They also allow small gaps where hot spent fuel can hide.

Removing carbon from the heads and pistons helps, as a hot piece of carbon makes a nice fuse for detonation to happen, and acts as an insulator, reducing cooling.

All of this wasn't much of a problem in 1970, when you could pull up to any gas station and buy leaded 100 octane gasoline. But today's gas isn't as detonation resistant. Cars now have computers, which sense when detonation occurs. How do these cars respond when this happens? In many cases, they retard the timing a bit. They also may enrich the mixture, as that will help cool the combustion chamber. But if the issue with the engine is that it isn't scavenging well enough, adding more fuel to the fire (if you will) isn't the greatest solution. If the engine is jetted correctly when there isn't detonation, making things richer at all times just leaves more fuel that isn't being scavenged and more material to build up carbon.