How much voltage drop is normal?

TAlber8

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chasing problems with bike running I believe may be battery. Runs for a few moments cold then dies, won't restart till sitting. Took me a bit to realize the battery was weak (kick only)

Kick only '74, pamco ignition, updated coils from mikes (the dual output black one). Original charging system.

Battery says charged 13v. Turn on key no lights and voltage quickly walks down under 12.4 ( 12.99, 12.98, 12.97...). Turn on lights drops to 12.2

Ok bad battery right? El-cheapo that is a few years old.

Put in good lithium battery from other bike to test. 13.3v. Also walks down but seems to hold out around 12.7.

Does that sound like a reasonable draw? A little concerned I have a short or bad ground to coils maybe?
 
If you had a starter motor, I would tell you how to load test the battery yourself. Since you are kick only, take the battery to a store that sells batteries and have it load tested. Battery voltage is not a good indication of battery capacity. Your voltages seem to be normal.
If you are getting a cold start on the fuel from the choke system, and then motor quits when you turn the choke off, that means the pilot circuit is not supplying enough fuel. Have you removed the pilot jet and confirmed it is clear? Is the float level set correctly? Have you read the CARB GUIDE that is in the TECH section?
 
:agree: well stated RG ! sounds like the old battery is still good....
sounds like dirty carbs to me too !....
...
Bob......
 
New vm34's set up by MMM. I checked everything before installing.

When I say running... I mean about 10 seconds. Never get to turn choke off. After that 10 sec it's pretty much game over.

Original carbs I was chasing issues of one cylinder with poor combustion. Couldn't track it down and I thought it was carb related. It sat for several weeks before I tried these carbs. (Fresh motor rebuild, cam chain good, valve lash good, timing was good.... it ran, just not well)

Going to try to run with other battery to atleast eliminate that... it's different polarity so I'll have to rig it up.
 
After market coils...........Why? ......when there are so many OEM coils available, used, with good reputations, at great prices, and so many different types available from different models?

Rant over, Scott
 
Still sounds like Carbs to me !....if it runs for a few seconds then dies it's running out of gas !
..... However it could have the spark dieing on you too....
get it to run again and when it dies turn off the gas to the carbs, then check and make sure you have spark.... pull the plug on both sides and be sure to ground the plugs and put the spark plug lead on them ....and crank it over you should see spark on both plugs at the same time.....
.....if you have spark ( good blue arc ) it's time to pull the carbs and see the fuel level in the bowls and clean the idle and choke passageways.... it doesn't matter if their brand new carbs... or not.... also make sure fuel is flowing to the carbs First, before you pull the carbs off !!!!
....
Bob....
 
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Its guess work until a methodical process is established...............If you know the battery is old and cheap, that is the first thing to remedy.......doesn't matter if that is not the main issue..........it could and will cause problems that can be diagnosed as carbs + a Battery in good condition, fully charged, is a must when doing any diagnostic work..........mechanical or electrical

Then onto other issues.......as suggested, pilot circuit is a cause of some symptoms described........

Going to get all sorts of claims from different people, this can cause confusion about what is the best way forward without jumping from one thing to another before isolating and sorting 1 issue then onto the next...............If you get to confused on who to believe do a check on the people giving advice, simply go to their profile page and look at their posts.

Also do some search/advance search, this helps to give confirmation of thoughts and ideas posted...........
 
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TALber8: when you say the battery is a diferent polarity than the original ...what do you really mean ? because that don't make sense
each battery has a negitive and a positive terminal !
anyway, you mentioned that you had it running ,just not good..... what were it's symptions ? was it dropping a cylinder ?
.....
....as long as a battery has 12v it's good to go in my opinion... the higher voltage is carry over from charging and a battery will drop fairly quickly from that OVER charged state.
when a battery gets to 11v it's time for a charge....
a lead acid battery will generate it's own electricity at 2vdc per cell with 6 cells that makes 12v however when you charge a battery you must put in more voltage than the battery puts out so 13 to 14 volts dc is common to charge with. 14.5v is getting kind of high.... and just goes to heat the battery .
j.f.y.i.
....
Bob.....
 
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I think he means that the +VE and -VE terminals are in the opposite corner to those on a stock XS650 battery and so the cables will be too short.

But....the problem does sound like carbs to me as well.
 
simple test to establish whether or not a starting/ running problem is a fuel supply issue.

Run the engine until its about to cut out and die then give it a squirt of Easy Start in the inlets.

if the engine picks up immediately and runs then the problem is with the idle fuel and air supply .
If the engine still dies with a squirt off Easystart then you need to look elsewhere.

use Easy Start as a diagnostic tool for checking suspected fuel supply issues ...its a quick, cheap and very effective diagnostic tool
 
Ahhh ! I see what ya mean Peanut ! because easystart or quick start over here, will make the engine rev up and continue to run
but if it dies anyway then it's gott'a be loosing spark.... good thinking and that's a easy quick test!
......
Bob.........
 
I never have starting fluid on hand. I do a similar test sometimes with a couple of drops of gas in the spark plug hole, checking for spark at the same time.

Scott
 
Ahhh ! I see what ya mean Peanut ! because easystart or quick start over here, will make the engine rev up and continue to run
but if it dies anyway then it's gott'a be loosing spark.... good thinking and that's a easy quick test!
......
Bob.........

Its an easy instant diagnostic Bob you can even use it to check for air leaks instead of propane or carb cleaner etc.

Another brilliant diagnostic tool that we all have and rarely use is the choke .
By applying varying amounts of choke to a running engine you can diagnose a weak or rich mixture at any throttle position. The choke is an independant supply of extra fuel so it doesn't alter any of the existing carbs settings but gives you an instant diagnostic .

i use the choke to check the WOT mixture under load to help select the best main jets on my bike and scooters
 
Yes I've done that before after porting a 2 stroke and have got the jetting purty much on..... wide open throttle and apply a small amount of choke and see if it picks up ANY.... if so your too lean ! obviously you need to be on the bike riding it and adding the choke slowly
....if there is an increase in the pull its a real good indication that you could go a bit richer on the main jet.!
.....
Bob.......
 
Ignition was good. Used an old plug and made a big gap and it fired no problem

The real culprit was new manifolds and gaskets had a poor seal. I used some gasketseer on faces and reinstalled.

1 problem down 50 more to go!
 
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