| Author | Message | ||
     Belanger |
i have a 97 s1 that the previous owner said had head work and a big bore kit. the bike only has 7k on the clock and seems to run ok but it does not pull as hard as i feel it should. it is a little quicker then then my night train. when i get to 5k rpm it flattens out and pulls slowly to the redline of 6. I'm thinking its a jetting issue but not sure any ideas? | ||
| Lynrd |
what carb are you running, and which exhaust? It may just need to be dialed in, which could be a long process to explain on an inter webs forum....and changes somewhat depending on the carb. If there is a local shop that does dyno tuning - that is the fastest way to get it just so. Otherwise, you will be "reading" spark plugs for guidance to tuning. | ||
| Phelan |
Could possibly also be a bad selection of cams, but jetting would be my guess as well. What kind of "big bore" kit? Like 1250cc or 1430/1475 (88/90")? | ||
| Natexlh1000 |
Your timing may need to be checked as well. Lots of headwork and huge displacement means next to nothing if the fire isn't being lit at the right time. | ||
| Belanger |
i don't have any info from previous owner on specs. i think its a stock carb. how do you set timing on one of these? | ||
| Lynrd |
You don't set timing at the carb, you set fuel air mix (aka jetting) with the carb. Does the carb have a round plastic cover on top of it? With four screws holding the cover on?. You do really want to be positive that you know which carb you are running - If someone spent the money for a big bore kit and having the heads done well, they may well have changed the carb to a Mikuni or maybe a S&S. The tuning principals are the same, but a Mikuni has a few more adjustment point. An S&S is dead nuts simple to tune, but my opinion is it a too large venture for street riding a 74" engine. Timing is set at the end of the camshaft, inside the timing cover. If you do not have a factory service manual for your bike, stop reading here for long enough to get one. I recommend a parts catalog as well - between the tweo most questions will be easily answered. Basic troubleshooting - only adjust one thing at a time. Make sure your timing is right per the manual - use a timing light and verify it is correct. I think your issues is in the carb rather than ignition in your case if it starts fine and runs fine until the upper end of the power band- but there is no point in adjusting a carb on an engine that is out of time. Assuming it is the factory carb, you have two fuel circuits - a "Pilot jet" and needle that meters the fuel coming in from off idle to about half throttle, and a "main" jet that takes over after about half throttle. Ride the bike for a while to get up to operating temp, stop, put in fresh plugs. Ride it again and get it up into the target tuning area - not from a RPM standpoint, but from a throttle position standpoint. Ride at that throttle position for a bit then, with out changing position, kill the engine with the kill switch. Pull over, and pull the spark plugs. They should be the color or ripened wheat. If they are darker - you are rich (or "fat') and need to come down on the jet size for that throttle position. If they are white, particularly white and blistered - you are too lean, which means you need to come up on jet size and/or you may have an intake leak. Bad things can happen if you run that way. That said, a basic approach I took from one of my mentors is "Lean it out, lean it out, lean it out until you are about to hurt something, then back up one step". this approach has served me well. Oily plugs means oil is getting into the combustion chamber. Bad news. Change the appropriate setting (mix screw, needle position) or jet on the carb, Install new plugs, rinse, repeat. This means when you start the process you have a pocket full of jets or a jet kit, and several sets of new plugs. Best practice is to start with the idle mix, off idle performance, quarter throttle, half throttle, and full throttle in that order. I use a strip of masking tape with witness marks on it to verify position. I use a big empty business park parking lot for thus operation and it can be a good way to while away a Saturday morning. The stock carb is easy to dial in - only two circuits. Some aftermarket carbs have 5 or 6 adjustment points. I have dialed carbs in this way for years, on both HDs and some two carb bikes. If you are meticulous you can really get to a fine state of tune. That said - when it came time to dial in my S2, I didn't have the time with my current schedule, so I farmed the job out to an excellent shop - JT&S, and Fireman Jim over there put her in a very fine state of tune - I could not have done better. So, there is something to be said with finding the right shop and using them for stuff like this, too. If you can't get the bike to pull strong all the way to redline, and it's is well tuned, you may be running out of gas in the float bowl. If that is the case - time for a Mikuni! After writing the mess above, I found this article, which says the same things but with more and better details plus it has pictures and stuff here http://www.nightrider.com/biketech/hd_cv_mods.htm . |
