04 Sportster 883 Carb Issues

Are you thinking that the MAP sensor needs replaced or the port where the MAP sensor is connected in the manifold needs cleaned?

not so much the port as the map sensor refrence port of the sensor itself its small and allways being hit with raw fuel then it sits and hot soaks in the manifold at shut down it needs to be checked! and if its cloged enough replaced. also the boot it sits in gets very gummy and soft and at times it will leak vacum as well and the refrence to the sensor gets to be inaccurate.

This is just for clarification and possibly my own education, but I have a different understanding of the MAP sensor. My understanding is that when the throttle is opened (low or no vacuum in the intake manifold) the MAP sensor tells the computer to (retard) the timing to prevent detonation. During part throttle cruse (vacuum present in the intake manifold) it tells the computer to advance the timing for better fuel economy and such. I believe this would also be true at idle; engine idling, timing is advanced, throttle opens and the timing starts to retard. If opened enough, the timing would go to whatever the (static) timing is set to on that engine. However, if the engine is not idling and is up somewhere in the RPM range, and the throttle is opened, I believe some advance would still be present based on what the particular timing curve is for that engine/computer configuration. In my experience, ignition problems usually show themselves at higher RPM’s and/or loads on the engine. That’s not to say that you shouldn’t cover ALL the basis though.

Not trying to sound like a know it all here; these threads are a learning experience for me and I just like to keep my facts straight. If I’m way off basis here, you ALL have permission to E-SLAP me!!!! :fight:

Regards…

that would be correct the map reads vacum and manifold pressure so if the port is restricted would in not be retarted!or scewed to think it retarted no diffrent in a speed density set up on a car if i see no vacum i richen the mixture a start backing off timing its no diffrent than a gm set up in fact its a gm delphi map !you are my freind 100 percent correct he is retarted if he is restricted !so as he snaps the throttle the module thinks he was allready there so it does not send any more advance intermittenly! thus the dreded carb cough!

Ok, that makes sense. I was not aware that this system would send advance intermittently when the vacuum signal was low, or falling off. I just thought it would start to advance as RPM increased and vacuum came back. I’ve never seen one of these running on a scope or anything so I have nothing to go by. I know these carb coughs can be hard to remedy. My 02 twin cam had a similar issue and I covered it with a bigger slow jet and a little extra idle mixture. Recently, I dropped the slow jet back down, installed a spring, emulsion tube and needle from Ken at CV Performance, as well as dropping the idle RPM to 900 and the cough is gone. That’s with a stock UN-DRILLED Harley slide. The bike runs good, I just can't get the MPG’s over low 30’s.

Jeff, keep us posted please. I’d like to know what finally cures it… Hang in there… :witsend:

Thanks!

Yes Jeff keep us posted....Thanks for the education BP....damn sensors...maybe one of these days I'll figure out a lot of mechanical problems are electronic

Guys I'm just saying to check it not replace it ! I don't know if that's the problem just trying to help .!

Ill post a map off my bike . It does change with rpm also . But its nothing like a voes switch timing map .wich does throw us off when thinking off a map sensor

How would you check it to see if its faulty??

Boys, this has been an education for me, though I run points/condensor ignition on my shovel. The newer electronics scared me off and I made the decision to go the old school route. Naturally, every system has its inherent problems, but I understand and can make roadside repairs with points/condensor/battery ignition . . .

Keep posting everybody - this is great stuff.

so they are using a map sensor instead of VOES in these years??

yep i have seen them as early as 1999

Learned something new today. Thanks.

I talked to a local motorcycle mechanic and he educated me on the dynojet system that was originally in the carb, I took it back apart and put in the drilled slide, the adjustable needle and the jets/emulsion tube that were all in the bike when I bought it, except the needle was not adjusted at the default position and the washers(spacers) were on the wrong see if the e clip. The bike will now only do the pop when not up to running temp. I figure I will making little adjustments possibly to fine tune but I am pretty happy with it now. Only problem is that I can't pinpoint the original source of the problem, ie manifold seals, carb boot, dirty carb, accelerator pump diaphragm, etc(all things that I replaced. Originally someone said remove the dynojet kit and put in stock parts, but it seems that this may be the only way for me to get the desired results. Thanks for all the posts, if I continue to have the problems I will return to this thread, but, I hope to never speak to you guys again, about my bike, no offense.