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Recent Update Nov2012: 74 850T

khudson24

Tuned and Synch'ed
Joined
Sep 13, 2011
Messages
28
Hey guys. Got my 850t back together, but having a running issue with it:

Fill tank up. Left petcock on only due to crossover. Take for a short spin, and return and everything is good so it seems. Next day, colder morning. Hooked up to batter tender as it seems it didn't quite want to turnover. waited. Starts right up again and I warm it up before departure. get on bike and head a mile down the road and it wants to stall out. I pull over and turn the rh petcock on as it appeared starved for gas (don't know why as I have a full tank). After a few cranks before depleting the battery, it starts up again. At next traffic light, acts like it wants to stall but doesn't. I turn around and head back, giving it throttle and all seems good. Turn into my street and it wants to die out but doesn't after I give it a quick throttle.

Couple things to note:

1) Stock carbs rebuilt and cleaned - all new parts to spec
2) New electrical system (stock) - charge light works properly and volts increase upon higher rpm
3) Tested petcocks with running water to make sure the on, off and reserve were working properly before install

This bike has been rebuilt from top to bottom.

I asm puzzled. The carbs are balanced and set up per spec and seems to start right up. I am guessing it is starving for gas over it being an elecrical issue. It is like the bike is running on reserve on one side, runs out and I turn the other side on and it does the same thing. But also not sure why it wants to stall out when slowing down at light or making a turn. Any suggestions? :?:
 
Re: 74 850T Running Issue

Did you check the screens on the petcocks? Also is the fuel cap venting like it should? Next would be to double check the float levels in the carbs.
 
Re: 74 850T Running Issue

Hey John, thanks for the reply. The gas cap was new from Mg Cycle. Need to check on that. The carb screens are clean. I tested the float height twice with it laying on its side and measuring with a caliper. I am leaving out of town today for a week, so I will have to review these issues next weekend. If you or anyone has more suggestions to test out, let me know.

Thanks....
 
Re: 74 850T Running Issue

BTW - just looked at my gas cap. Under the lid is a tiny hole which looks to be for venting, so I don't think this is the issue. See pics:

IMG_20120925_140317.jpg


IMG_20120925_140157.jpg


Also, trout sent me over the float adjustment instructions (lie carb on table and measure 24mm between bottom of float and casing lip), which I did.

When I get back I'll have to drain my tank and take a closer look at the screens and crud possiblity in the tank. Although I took them out a couple of times already to make sure the petcock was working and flowing correctly per the on and off positions.

Anything else I can check when I get back nest weekend?
 
Re: 74 850T Running Issue

Sounds like this is happening at low speeds & at cruising speeds but she will accelerate ok??

I agree it sounds like fuel but the low battery tweaks me a bit. Possible there is low voltage at low RPM to the ignition causing a spark loss? Is the ignition switch new? May have high resistance causing a power drop. Under acceleration the charging system may be putting out a high enough current to overcome a resistance in the switch or some place else. Long shot I know but it sounds like you have the fuel system down pat. An easy check here would be to make a jumper wire to go from battery positive directly to the coil plus side (opposite terminal the distributor connects to) and see how it runs. Be aware if you ride it the only way to shut the engine down is by pulling the wire off!!

The only other fuel related things I can think of would be a weak choke slide spring or a choke slide that is sticky or worn and holding a choke open. If it is partially opened or closed acceleration would overcome the richer fuel but at cruise speed or idle it may start to foul the plug.

Are the carb slides synced to come off idle at the same time?

Did you adjust the carbs by pulling a plug wire off one cylinder and diddling the other carb? It may be just be carbs are out of adjustment.
 
Re: 74 850T Running Issue

Have a look at your spark plugs to see if they give any indication. You are looking for a normal color, if anything else - excessively black or white then that could give a clue if it is fuel related.

If you suspect the venting of the fuel cap just go with 1/2 a tank of fuel and the cap released around the block and see if things are any better.
 
Re: 74 850T Running Issue

OK guys. I have just returned from vacation and I plan on testing your suggestions out tomorrow. I have a question regarding the battery as tewrecks suggested. It was a new odessy battery that I put in a few months ago. I was having charging problems and had find the culprit. But the battery went through much faster charging many times on my charger, not the normal trickle setting. Could this kill the battery? I ask because when I initially got the bike back together, it was running fine, no weirdness as described above, that it until I realized the battery was not charging and found that my rectifier was toast. The point I am making is that it drove farther distances with no other problem. I replaced the charging system completely (rectifier, regulator and alternator). Charging light operates normally, and higher rpms feeds the battery with increased juice. But now it gives me fits as I drive a block away.

Just wanted to get your thoughts before I go out and get a new battery or something.
 
Re: 74 850T Running Issue

A lot depends on the charger you used on your battery. I used to have a very expensive charger that didn't monitor the batteries condition. It charged, it trickled, it fried a couple of batteries for me. You also have to make sure you don't use a charger designed to charge car batteries unless it has a lower amperage setting for motorcycle batteries.

Can you take the battery to a Sears or an AutoZone type place and have it tested? Its free and would answer at least one question for you.
 
Re: 74 850T Running Issue

Pokeyjoe & tewwrecks both said it & I agree. Start with the battery & while it's out wiggle all your connections.

By the way that is a good lookin T. I'm really hopping to be able pull mine down this winter and give her the long over due going over.
 
Re: 74 850T Running Issue

UPDATE:

Ok. Had battery tested at Batteries Plus - holding charge, accepting charge and tested good under load. I retested rotor and stator and all is good. Charging light still functions properly. Checked float height - all is good. Fuel is coming out of petcocks freely, so not clogged. Also, drained tank to 1/2 full. Rechecked connections to new coils & spark cables (mg cycle) and were good. Took out spark plugs, rechecked gap - good.

BUT... plugs were black/carbon like, evidence of too rich of fuel mixture, right? Cleaned them off with a wire brush. Put back and started bike. Started right up with chokes on and was letting warm up before I take for a short spin. Let chokes off and still running under normal rpm. About to take for a spin and stalled out. Would not start again. Battery is still strong.

I am deducing this has to do with spark since fuel seems fine and electric/battery system seems fine. The carb mixture screws are approx. 2 - 2 1/4 turns or so out on each side from fully seated in as manual states. So is this engine burning too rich fouling out the plugs? If so, just replace plugs and turn out mixture screw more? If so, what is the best procedure so I don't keep fouling plugs out and worrying if I get stranded down the road with carbon buildup? Or I am off and need to check something else? Let me know. Thanks so much....
 
Re: UPDATE: 74 850T Running Issue

Where it is a time issue, it sounds like something is breaking down when it gets hot. Yes you have new coils, but this is possibly an ignition failure mode and stopping to work when hot is a coil failure symptom. Coils tend to work until they get hot and then fail. Next time you start the bike and she dies, pull the leads and make sure you have spark on both sides. This will tell you if it is coil/ignition related. Are you running points and condenser? you may be having a condenser issue as a possibility. Also just for our information, what are your carb jet sizes? Also make sure the enriching circuit plungers seat when to close them. Most Ts just need the enriching circuit to start, once started you shouldn't need it and they should be shut off. Leaving the enriching circuit on too long can foul your plugs.
 
Re: UPDATE: 74 850T Running Issue

John got his reply posted before I did so this is kind of a repeat with some testing you can do.

Possible chokes are not returning or seating correctly. The choke slides can get worn & sticky and the springs can get weak. Make sure your cables are adjusted and not binding.

The springs are about the same size as a ball point pen spring. Might try getting the bike warmed up then shut her down. Pull the choke slides out of the carbs and replace the springs with heavy springs. Shoot WD40 right into the hole where the slides go and all over the slides. Re-Assemble and start the bike. What you are trying to do is make sure the slides stay all the way down and are not choking.

If the bike runs properly then it is the chokes. At MG Cycle you can get new slides & springs or flip lever replacements.

Have you tried racing the engine during warm up?
Does it run ok with the chokes on then stumble when they are off?
And as John said check the jet size.

Now that I have said that I'll shoot a big hole in it or look at it another way.

If both plugs are fouling then I tend to go back to an electrical problem that affects the whole system. It's doubtful that both choke assemblies failed at the same time just like two coils going bad at the same time. It can happen, it has happened but not often.

Check your wiring schematic and see where the feed wire comes from for the coils. Is it directly from the switch or the kill switch?

I think I suggested earlier to make a jumper wire and feed the coils directly off the battery. If that works then it is in the wiring before the coils. Ignition or kill switch with high resistance or shaking loose. If it dosen't change anything then closely check the wires from the coils to the distributor and also where the wires go under the cap to feed the points. A loose cond wire at the points can cause it or a loose cond, try wiggling them to see if they are tight, they will also fail under heat.

Might try starting the bike with air cleaners off and twist the throttle to the break up point then try squirting carb cleaner in the carb. It's not a great test & does not prove electrical or carb but it is another piece of data to add. The carb cleaner may smooth it out or keep it running which can indicate a lean fuel condition or a weak spark.

I'm about to run out of ideas but I will think about it some more.
 
Re: UPDATE: 74 850T Running Issue

Just wanted to FYI : the carbs were cleaned and completely rebuilt with ALL new parts from MG cycle with stock jets and even choke slides. The coils are also new from MG cycle. Cables are not binding and are synched. How do I test the coils? I need a step by step if someone has it. I am green to this area of the bike. Thanks,
 
Re: UPDATE: 74 850T Running Issue

If the plugs are fouling causing the engine to stall than that condition can either be a cause or a result. I don't know if you've performed a compression test? But if your rings are bad there could be a situation in which too much oil is getting into the combustion chamber passed the rings. Alternatively if your ignition system becomes marginal than the plugs foul up with excess fuel.

If the coils have overheated once it's possible that they are now bad coils. Even though they may not fail the ohm test in spec they could still be bad as they warm up. The coils should be warm but not so hot that you cannot touch them under normal operation. Also if you have spare coils you could try a substitution even if only on a temporary basis. Another option here might be to try a hotter plug. Not sure if you're running your coils with or without a ballast resistor? If a ballast resistor is called for, you could temporarily bypass the ballast resistor to see if there is any change. If a ballast resistor is required and you're not running it that could overheat the coil as well.

http://www.boschsparkplugs.net/411_manufacturer.asp

Also I've seen the situation where the coil housing fails with an imperceptible crack and as it warms up secondary current leaks shorting out the coil. You might be able to see this in the dark. Of course if the bike is stalled it might not be evident while you're trying to start it.

Ignition timing is correct?
 
Re: UPDATE: 74 850T Running Issue

khudson24 said:
the carbs were cleaned and completely rebuilt with ALL new parts from MG cycle with stock jets and even choke slides.

Atomizers and slide needles too?
 
Re: UPDATE: 74 850T Running Issue

Bike now won't start at all even with gas and juice. Has to be related to spark. Attempted to hook up the coil positive directly to battery positive. It let out a noise and sounded like it was expelling compressed air and a very thin poof of smoke. Any way, pulled out coils. The left coil had a big dent (which wasn't there prior as they are new) and a filmy, no odor grease like substance on its shell. Definitely coils and I probably really fried it now . I think they were overheating because just before I couldn't start the bike no more, that light thin smoke appeared. I thought it was from alternator, so I doubled checked that and all was fine still. I have the older ones still so I will hook those up. I want to go over the static timing again with the replacement coils. Since the points are removed as I have a Dyna III, where do I connect the positive test lamp lead - to positive of coil terminal? Just need verification - which side of the coil is positive, what the dyna III connects to or the other side? Once I confirm statically with replacement coils, I will start up and verify with timing light.

Unfortunately I have no real knowledge regarding a ballast resistor or how to tell if it has one or needs one.

NOTE: When I bought the bike last year to restore and prior to even laying a wrench on it, occasionally I would hear that sound as described above when I turned off the engine. It happened rarely, but that was THE sound it would make. Always started right up and ride fine.

The input about what you guys stated about the coil getting too hot - I am recalling that on my first ride from completing the rebuild, I took the bike out - started right up. After about 40 minutes, the bike acted really funny like it wanted to stall and was jerky. I realized my charging system was working as it depleted my battery. Charged battery at auto garage and got home. Worked on charging system and all good. However, there were probably simultaneous problems - charging AND coils. Once I fixed the charging I thought all was well, but it was both. Sound about right?

I think that was the problem all along as everything else was gone over even if I just exacerbated it :oops: :oops: .
 
Re: UPDATE: 74 850T Running Issue

BTW - yes new atomizer - mean everything on that carb. Also, new rings and piston kit and compression is good, I think you guys nailed it with the marginal ignition fouling out the plugs. If I just replace coils, will the same thing happen again even with fine tweaking the timing/condensor?
 
Re: UPDATE: 74 850T Running Issue

khudson24 said:
BTW - yes new atomizer - mean everything on that carb. Also, new rings and piston kit and compression is good, I think you guys nailed it with the marginal ignition fouling out the plugs. If I just replace coils, will the same thing happen again even with fine tweaking the timing/condensor?

With the Dyna there are no condensers. To test coils requires something like a Sun engine analyzer. These are now rare as hen's teeth. If you have oil leaking out of the coil(s) it is toast. Toss them. I believe Dyna now recommends 5 ohm coils with their ignition system. I'd suggest getting the Dyna coils as they are very robust and don't require a ballast resistor.
 
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