Sporty Carb help

[jgc2521]

Hey, I have a 2002C with the 1250 nrhs kit, stage 2 headwork, N8 cams, Ultima singlefire ignition, forcewinder intake, and SE slip ons. I have been trying to tune in my carb and havent had any luck. I have an older CV carb from my old 883 bike and decided I would slap it on while looking at the carb on the 1250. Well to my surprise, on my test ride the bike came to life as compared to the old carb. much better performance. I timed the bike at 28* a right before switching the carbs.

Before i timed it with the light I had the bike running decent, just low on power and not lively. after timing it at 28* i had a box of bolts (sound) while accelerating. with the bone stock carb it ran better.

I took apart my 1250 carb and it has a dynojet kit (?)
-adjustable needle w/ the E clip in the 4th slot from the closer end, with 3 washers closer to the end.
-emulsion tube with only 2 holes
- 45 jet
- 180 jet
- I don't know whether it has the stock slide or not.

I don't have any other jets for the carb so I was wondering if I should modify the bone stock carb or this one w the what i assume to be dyno jet kit in it.
If it is dynojet i assume it would be the 8103 kit.

The bike is running better with the bone stock kit that it has since i've done the upgrades so i was assuming getting a few jets from harley would be the way to go.

Anyways I got 2 carbs, a dynojet kit and want to make one good carb, what would y'all recommend doing? The bone stock carb doesnt even have the cap drilled out on it. I was thinking just do some test with it on there but I would value y'alls responses for the best course of action.

-Couch

[patrickd]

Sounds like with the rattle you might be running too much timing for the level of compression in your cyls.. When you hear that sound you're killing your engine.. Either step up the octane or retard the timing till it is quiet again.

[jgc2521]

Originally Posted by patrickd

Sounds like with the rattle you might be running too much timing for the level of compression in your cyls.. When you hear that sound you're killing your engine.. Either step up the octane or retard the timing till it is quiet again.

When I put the stock back carb on the rattling stopped completely. Also isn't a stock sportster set at 35*?



Also, forgot to mention. The modified carb was done by the previous owner along with him guttind the mufflers, and buying the N8's... he blew his motor and i bought his complete bike (pile o parts) for cheap cheap. I used his frame to put my built motor in and used his cams, carb, intake. I've added the singlefire later, and am just getting around to tuning this thing to it's potential.

[patrickd]

yes. It sounds like you prob had a plugged carb and it was running lean and causing that spark knock.

[maru]

Id work with the stock carb. See what it has for a pilot and a main jet and stick with keihin stuff on the new carb if possible. It sounds like you have a dyno jet needle jet. Those only accept their main jets and they are not marked the same as the oem jets. In other words a 180 main jet by dyno jet is not the same as a 180 keihin jet. Depending on how long ago the kit was made, the needle and needle jet could be prone to wear.

Put a fresh set of plugs in the thing, ride it and see how it behaves. If it is rattling with the new carb on high test, pull some timing out of it before you hurt it. If the bike runs good, don't assume you need to throw jets at it unless you have some indication that it needs it.

[jgc2521]

with my CR 10.5:1 i've been running ngk dpr8ea-9 at .040 does that sound right?

[maru]

DCPR8 - I think the stock ones are 7's. I am not sure where the DPR8's are different.

[jgc2521]

i believe the 8's are one heat range colder than the 7's... that is to make up for the high c/r.

[XLXR]

Rubbermount_EVO Carb basics and jetting by reading the plugs

This thread is buried in the jetting sticky index.

Sounds like you need to understand basic tuning methods. The link above outlines such a method. However, it is slanted to rubber mounts with stock ignitions.

The rattling you hear is probably pre-ignition or detonation, which can be very dangerous because it can damage pistons. Your first step is to retard the timing to prevent it from happening.

Then do plug readings at idle, mid throttle, and full throttle to determine how to change the jetting. Once you get good plug readings at all three throttle positions, start to advance timing a few degrees at a time.

High compression engines will need premium octane gas.

You probably should go back to 7 heat range plugs. Colder plugs are not meant to cure the problems you are having. Use anti-seize on the plug threads, just a thin coat to prevent getting any on the electrodes.

Next question, does the 883 carb have the same throat size of the other carb? It is possible the 883 carb was previously jetted too rich, and it just happens to work on your 1250. At least it works better than the other carb.

Seems like a lot of people have problems with the Dyno Jet kit. Certainly, a lot of the problem is not knowing how to tune correctly from the start. If the carbs you have both have the same throat size, I would start with the one that works best because it may need nothing more than a few jets and needle. No telling how many other problems the other carb has.

[jgc2521]

Originally Posted by XLXR

The rattling you hear is probably pre-ignition or detonation, which can be very dangerous because it can damage pistons. Your first step is to retard the timing to prevent it from happening.

Yeah, it was detonation for sure. Once i heard it i decided to put the virgin carb on bf something happened. The virgin carb cleared it up and i looked into the dynojet carb

Originally Posted by XLXR

Then do plug readings at idle, mid throttle, and full throttle to determine how to change the jetting. Once you get good plug readings at all three throttle positions, start to advance timing a few degrees at a time.

If only it would stop raining

Originally Posted by XLXR

High compression engines will need premium octane gas.

already do

Originally Posted by XLXR

You probably should go back to 7 heat range plugs. Colder plugs are not meant to cure the problems you are having. Use anti-seize on the plug threads, just a thin coat to prevent getting any on the electrodes.

OK, please explain. don't take me the wrong way i want to learn. these were just the plugs that Dan had recommended for what i have so i took it as gold.

Originally Posted by XLXR

Next question, does the 883 carb have the same throat size of the other carb? It is possible the 883 carb was previously jetted too rich, and it just happens to work on your 1250. At least it works better than the other carb.

the 883 is virgin, i haven't looked to see what jets are in it. But it does work better from the short ride i have made since the switch

Originally Posted by XLXR

Seems like a lot of people have problems with the Dyno Jet kit. Certainly, a lot of the problem is not knowing how to tune correctly from the start. If the carbs you have both have the same throat size, I would start with the one that works best because it may need nothing more than a few jets and needle. No telling how many other problems the other carb has.

I assumed the throat size is the same. They both fit in the same intake manifold, and are both factory carbs. one is off of a '95 883 hugger and the other off of a 2002 1200C

I'm more of a diesel guy. I know my way around motors, just never really dealt with hopping up a bike before.

I plan on riding the bike with the virgin carb for a little while with fresh plugs to see how they look. Then getting new jets from there.

Do i need to be worrying with the timing since i'll be changing the jets and all. right now I have it set at 28* that was with the molested carb.

I also adjusted the voes after building my engine, I just can't remember what i set it at. I went with something that I found on here so hopefully it's good for now.

Thanks for the in depth reply!