weird engine issue dies at higher speeds

[deshi]

just rebuilt the engine for my 83 650 special, also rebuilt the carbs and replaced a bad rotor. the battery still might be shit after all the previous problems and recharging of it over time. Bike runes fine, idles perfect will run great till i get over 40mph then suddenly it will die out. I switched the petcock to prime in case the vacuum was acting up and that didnt resolve it. I have not tested the battery for a bad cell or anything i wanted to ask on here before I did any work as i asked before and that led to rebuilding of a lot of stuff but the advice was rock solid and dead on. can a bad battery be causing this issue? I only kick start as well and everything is stock.

 

[jayel]

open the gas cap right after it dies, sucking sound means fuel vapor lock (blocked vent in gas cap) are the carb atmospheric vents clear to outside air? putting to long of hoses on those vents can cause weird problems too

 

[deshi]

actually yeah i hear a sucking from the gas cap even without opening it. i didnt even think about the vent so is that the petcock filter that could be causing that? the valve vent hose was missing when i got this bike and my father in law is a mechanic and he made a new hose and we ran it to the top of the filter box instead of the bottom could this of also caused that issue? i will go remove that hose all together and do a test rev and see if that solves it.

 

[deshi]

OK ran a test with the cap open and same results, idles great after a high rev it just cuts off and dies. also tried same test with filters out.

 

[deshi]

I know the battery most likely has a dead cell it will not really charge past 10.5v so I know that is probably one of the problems, it just seems weird that it will kick over and idle but if i rev it will just die, now earlier today I had it on a charger while swapping out the rotor (which did fix the charging system problem I had earlier), and i had 12.2v idle and 14.3 or so while at 3k rpm so i know the charging system is working good, however after a short 20 mile ride i was stranded and finally made it home and voltage was down to 10v.

 

[Brian902]

You solved your own problem, now go fix it.

New battery please!

Last question, must have been you, I don't smell it up here.

 

[jayel]

actually yeah i hear a sucking from the gas cap even without opening it. i didnt even think about the vent so is that the petcock filter that could be causing that? the valve vent hose was missing when i got this bike and my father in law is a mechanic and he made a new hose and we ran it to the top of the filter box instead of the bottom could this of also caused that issue? i will go remove that hose all together and do a test rev and see if that solves it.

not a problem with the petcock, the gas cap itself has a vent to allow air into the tank as the fuel is used, the bike will act like it's running out of gas (which it is) ... low voltage will also cause the problem as the TCI needs a good stable voltage, replace battery and try again,

 

[deshi]

Thanks guys I am going to go pick up a new battery tomorrow is there any advantage to a standard battery or an AGM?

 

[jd750ace]

Go AGM if you can. They don't belch acid! Also, follow all the instructions with a new battery, regardless of type. Take your time with it and make sure it stabilizes. If you buy a dry shipped battery and charge it yourself, this is very important stuff. The initial acid load will generate a good bit of heat. The battery will go to around 140-145 degrees, and must cool and stabilize before topping it. It will usually "show" a full charge with a meter at that point, but it needs a deep cycle charge to get it up to full potential. That can take a good while. took mine nearly 7 hours. If it's a wet battery, it gets topped off at that point, AGM, none. Never add anything to an AGM battery that did not come with it. You're close, now make sure you get a good battery together to finish the summer off with.

 

[scabber]

The agm doesn't require you to check or add water or spill other than that The agm battery CCA can be larger than the lead acid. I have had the lead acid battery last longer than the agm. The stock size battery works.

 

[deshi]

Thanks for the advice jd750ace i been working on this bike the last 3 months and this is the final bit of work. I feel accomplished after rebuilding the engine on my own, and the carbs, and the charging system is brand new now. guess it was just that damn 2nd hand battery i figured my father in law had bought a new one and today he told me he don't even remember who he got it from and after pulling it out i can see it is about 5 years old and looks like shit. sometimes the most simple thing can cause a headache for weeks. Eventually I want to go with a pma and pamco ignition.

 

[deshi]

I am just planning on hitting up advanced auto parts since they have agm or lead acid in stock just down the road.

 

[deshi]

ok replaced the battery and went for a test ride today and the same darn issue happened, i got about 15 miles out and it just up and died like it was not getting fuel, got back tested battery its at 10.5v, battery was charged fully before use as well. bike has a new rotor brushes stator, and mikesxs rec/reg unit. Could this be something from the keyswitch causing this issue? that is the only thing we were unsure of. tested all circuits elsewhere and its all working fine ohms are great on rotor, and stator test shows that is fine. the rec/reg was not re-tested since we bought a new one and tossed it in but i guess that could of been toasted again at some point after i was test riding. i finally got a job and will need my bike to get to work next week so i am still hoping this can be fixed in time, and i must say i plan to switch to a pma/pamco asap. Also could the ignition cause this problem as well. I have a box of a few ignitions that the PO gave me one was a weird high performance never seen it before its chrome and has a higher output than the 2 stock ones I have so I didnt put that on I was unsure if that would damage anything with the higher output. we glass beaded all the connectors as well to be on the safe side and replaced some in the process.

 

[Einherjar]

i would get to the battery and charge it back up. then get your volt meter. start your bike up. then check the voltage at the battery at idle, then check the voltage at 2000 and 3000 rpms. then report back with the numbers.

 

[deshi]

i did that test earlier and at idle it was 12.8 roughly and 13.4 at rev. replaced rotor, stator tested good and replaced the rec/reg still same issue wondering if it is the ignition or bad pick up coils now?

 

[Einherjar]

13.4 is low at revs.
It does not sound like a ignition problem when the battery is dropping down to 10.5 volts
i think charging system problem or a short in wiring somewhere

 

[deshi]

not sure what else to check not sure how to test the pickup coils that is pretty much the only thing I have not tested yet. and the keyswitch test in curleys guide confused the crap out of me.

 

[NONclow]

Condition of grounds at battery, engine, fuse block, rectifier/regulator???

 

[deshi]

ok replaced the battery it is good charging system working now just fine replaced ignition as well but it runs for a bit then just dies like it lost fuel but no sputtering. rechecked carbs they are totally spotless and clean was cleaned very very well by a carb specialist after me and my father in law also had cleaned it just to be sure. gas cap vent is functional and fine, petcock is fine fuel getting to float bowls fine. running out of crap i can check to see why it just up and dies off. if it sits overnight it will run for about 20 minutes then dies then after that it just runs for a bit and when you let off throttle just poof cuts out. have not tested pickup coils yet doing that tomorrow. anymore suggestions?

 

[NONclow]

Carbs were cleaned.... obviously.... what about proper float height/needle & seat condition?