Engine not reving above 5000, except in neutral - 850 T3

[Tamas Jovanovics]

Hi Guzzistis,

My T3 starts and goes fine in town, but on highway I noticed that it struggles to rev beyond 4800 (in fifth gear). At the point of stuck, it starts of kind of hesitating, it's not like one cylinder would not go, it's rather a strange near-interruption feeling. Interestingly though when I pull the clutch (as soon as the issue starts presenting itself at around 80 mph) to see if it can rev up without being in gear (like in neutral) it revs up fine till 6500 (possible also beyond, but wouldn't like to do that to her).

So in neutral it can rev up nicely to any regimes, but in gears less and less.

So I checked the acceleration in all gears, and in 1st gear it still reaches about 6000, in 2nd 5700, in 3rd 5300, in 4th 5000 and in 5th 4800 (which is around 130 km/h).

On a theoretical level, what would you suspect might be wrong? I would obviously start with checking spark plug, carburetors, and then maybe advance, but given that the issue is not present in neutral, I kind of suspect the coils.

Basically my question is would you be checking electrics or fueling system first in such case?

I know that such old carburetors run rather fat, but since I have the K&N filter (the original shape in the original housing, not the the two separate cones) installed, that should be compensating it, as it allows more air flow. (Carburetors have been thoroughly cleaned 2-3 years ago and I always make sure there is no fuel left in them when the bike stands for longer periods over winter, so we should be able to exclude that something is stuck).

Would be grateful for any pointers. Many thanks in advance.

Best regards,
Tom

850 T3 California
(& Griso 1100)

 

[john zibell]

Had a similar issue with my T3 when I owned it. Just for chuckles after the bike was totaled (car left hand turn into me) I checked the cam/valve timing. Discovered the valve timing was not correct by several degrees for one of the cylinders but correct for the other. Don't ask by how much as it was in the 1980s and I've lost that brain cell since then.

 

[Trout]

OK. If I am reading & understanding correctly the problem is only present under a load (in gear).

If you can try this without getting in trouble you could block the front wheel (put it against a wall) & lock the front brake then put the bike in first or 2nd gear & slowly let the clutch out a little bit (slip the clutch) while increasing the engine speed.
In other words verify that it is happening under load & also see if you can determine if it is consistent at a specific RPM.

Is there any back firing thru either the exhaust or carbs?
Is there any black smoke from the tail pipe? Both sides or just one?

My avatar is a bike I got real cheap because "nobody could figure out why it don't run right".
Long story short: Somebody had been into the carbs and lost the choke spring on the left carb.
Bike would idle fine, rev up when not under a load but going down the road would begin to lose power.
The choke slide without the spring was moving and dumping fuel.
That's why I ask about the black smoke because I saw smoke coming from the left pipe.

If it is backfiring that can be a good sign that it is timing (as John stated) or electrical.
Bad ignition points and/or loose/bad condensors or weak coils could cause what you are describing but would generally show up on one cylinder but not the other.
Again, if I understand your post it does not seem to be specific to either side but an overall issue.

Many times when electrical stuff goes bad it will cause backfiring.
When the power is turned off & then turned back on there can be enough raw gas in the cylinder to cause the backfire & depending on which valve is open it may blow thru the exhaust or back thru the carb randomly.

if it is backfiring consistently thru either the exhaust or the carb then many times that will indicate a timing issue.

I always start with looking for the simple solution & with basic, easy to check stuff.

Check your timing using the marks on the flywheel & a straw down thru the spark plug hole.
Wouldn't hurt to pull the valve covers off & check valve clearance also.
Then check your ignition timing against the flywheel marks.

Post again.

 

[john zibell]

Trout,

That "test" seems a bit tricky. Wouldn't be easier and safer to just pull the enriching assemblies to check for the spring. With valve timing off, the beast would run fine. No black smoke or back firing. However, you hit the wall at about 75 to 80 mph in 5th gear. Going to 4th you can gain a little, but under load you just don't have the power.

 

[Tamas Jovanovics]

Hi Trout

many thanks for the extensive reply.

Yes, the issue appears onlu UNDER LOAD, and as said, more and more so with the higher gears.

The bike starts cold and hot fine. Idles fine. Rides very well in town and outside town. I only realized I have a problem when I rode on the highway and wanted to exceed 4800 rpm in 5th gear. The bike also seems to lose power in 5th gear when the road starts to go upwards, on slopes. But there is no back-firing at all. And no black smoke neither.

I rather feel a hesitation, like if you turned off the ignition for a micro-second or like you would brake for a micro-second whilst you keep pulling the gas. Sometimes the phenomenon even happens at lower revs, around 4000 rpm. However, when I get on the other side of the slope, going downwards, the bike revs up easier till around even 5500 rpm.

You are right, I have to check the carburetors and the check the timing.

Regarding the carburetors, am happy to touch them. I cleaned them 2-3 years ago and maybe when I reassembled them I did something wrong.

With the adjusting the points, I am more afraid of. In my 22 years of owning Guzzis with points I have never done this operation (my LeMansIII was working fine for 14 years without touching it) and my Haynes Owners Workshop Manual's description is slightly Chinese for me. I used to have a French Workshop Manual for my LeMansIII and I remember in that one it was explained really well with many photo illustrations.

Does anybody have a link to how to check and adjust the points? I would love to this job as I think it shouldn't be much more complicated than adjusting the tappet clearance, an action I have done dozens of time.

Many thanks for any further tips.

Kind regards
Tom

OK. If I am reading & understanding correctly the problem is only present under a load (in gear).

If you can try this without getting in trouble you could block the front wheel (put it against a wall) & lock the front brake then put the bike in first or 2nd gear & slowly let the clutch out a little bit (slip the clutch) while increasing the engine speed.
In other words verify that it is happening under load & also see if you can determine if it is consistent at a specific RPM.

Is there any back firing thru either the exhaust or carbs?
Is there any black smoke from the tail pipe? Both sides or just one?

My avatar is a bike I got real cheap because "nobody could figure out why it don't run right".
Long story short: Somebody had been into the carbs and lost the choke spring on the left carb.
Bike would idle fine, rev up when not under a load but going down the road would begin to lose power.
The choke slide without the spring was moving and dumping fuel.
That's why I ask about the black smoke because I saw smoke coming from the left pipe.

If it is backfiring that can be a good sign that it is timing (as John stated) or electrical.
Bad ignition points and/or loose/bad condensors or weak coils could cause what you are describing but would generally show up on one cylinder but not the other.
Again, if I understand your post it does not seem to be specific to either side but an overall issue.

Many times when electrical stuff goes bad it will cause backfiring.
When the power is turned off & then turned back on there can be enough raw gas in the cylinder to cause the backfire & depending on which valve is open it may blow thru the exhaust or back thru the carb randomly.

if it is backfiring consistently thru either the exhaust or the carb then many times that will indicate a timing issue.

I always start with looking for the simple solution & with basic, easy to check stuff.

Check your timing using the marks on the flywheel & a straw down thru the spark plug hole.
Wouldn't hurt to pull the valve covers off & check valve clearance also.
Then check your ignition timing against the flywheel marks.

Post again.

 

[john zibell]

Points aren't that difficult. Set the gap with a feeler gauge. For the fixed set you rotate the entire distributor assembly to set the timeing for that cylinder (it has been so long since I've done one I don't remember which side, just trace the wire from the points to the coil will tell you) then move the mounting plate for the other cylinder to time it. Sometimes you may need to vary the point gap a thousands or so to get both cylinder in time. The marks on the flywheel are usually close enough to set initial timing, however it is full advance that is needed and best to check that with a timing light. Since it is a T3, the advance springs may be original. I'd recommend replacing them before you set the points and timing. They are located under the plate the points are on.

 

[jr1967]

Another thing to check is to drain both carburetors into a glass jar and see if there is water present. Water will clog up your jets under acceleration. Your tank might have a layer of water in the bottom, so just draining the carbs might not solve the whole problem.
And check for any corrosion in the kill switch, under load your spark might be just too weak to ignite the mixture properly.
Two quick easy checks to rule out these possibilities.
Good luck. JR

 

[Trout]

Trout,

That "test" seems a bit tricky. Wouldn't be easier and safer to just pull the enriching assemblies to check for the spring. With valve timing off, the beast would run fine. No black smoke or back firing. However, you hit the wall at about 75 to 80 mph in 5th gear. Going to 4th you can gain a little, but under load you just don't have the power.

John,
After re-reading my post I agree and probably should not have suggested it.
I was just trying to give an example of a way to determine some facts.

 

[abbienormal]

One thing I always check first in these situations is the airbox/airfilter. You never know if some critter has tried to use it as a storage depot. Also I have seen that rag that is stored under the seat covering the inlet or sucked into the inlet.

 

[Tamas Jovanovics]

Thanks for the suggestion.
I am more and more sure it is a carburation thing and not ignition (points-timing).

To the suggestion of some, I checked the valve tappet clearence. Indeed, on one side, the gaps were way too small (a Guzzi mechanic changed my cylinder head gaskets 3 years ago. It happens to me the second time that a mechanic is not setting up properly the tappet clearence).

I set it up properly to the required 0,22 and went for a ride on the highway. No change at all. Engine revs up fine and easy when in neutral but under load above 4-5000 it starts to get blocked, to kind of 'die off'. But no missfire, it feels more like the cqrbs don't get properly fuel. To experiment a bit, this time, when I reached the critical rev (around 4000 in fifth), instead of releasing the gas, I was pulling it further to max. And then the engine completely died off (it really felt like it gets lots of air but no fuel to explode). All this was just a second or two, immediately after I released the gas to 4000 and the bike went further.

At this stage I decided I will have a look at the spark plugs. So at 4000 I pushed the clutch and the kill switch at the same time. After rolling out the bike I checked the plugs and left seemed exactly as mid-light brown as it should be, whereas the right was a bit too much light brown (almost whitish). But not sufficiently to explain the full die-out at 4000.

So now I suspect that jr1967 light be right and I have either some water left in one (or both) of the carbs left after the extensive cleaning from a few years ago, or I have water in my tank. I am not with my bike now so can't check, but in week or so I will be able to report about my findings.

In the meantime, many thanks for all the help and suggestions. It really makes searching for the issue easier.

Best regards
Tom

Another thing to check is to drain both carburetors into a glass jar and see if there is water present. Water will clog up your jets under acceleration. Your tank might have a layer of water in the bottom, so just draining the carbs might not solve the whole problem.
And check for any corrosion in the kill switch, under load your spark might be just too weak to ignite the mixture properly.
Two quick easy checks to rule out these possibilities.
Good luck. JR

 

[Tamas Jovanovics]

You are right. I need to check that too (even though I have the original - very unconfortably accessible - air filter box with K&N replacement filter) but I now need to check it all: carbs and tank for water and airfilter for any strange objects there.

Many thanks again
Tom

One thing I always check first in these situations is the airbox/airfilter. You never know if some critter has tried to use it as a storage depot. Also I have seen that rag that is stored under the seat covering the inlet or sucked into the inlet.

 

[john zibell]

It still sounds like a valve timing issue to me. This would be from an improperly made camshaft. Ignition timing and carburation can be perfect, but if the valve timing is off, you will get what you are observing. You will need a degree wheel and observe when valves open and close. You will need a service manual to perform the valve timing checks.

 

[Tamas Jovanovics]

I hope John you are not right with this. Why would the engine then still rev up easily in neutral?
I also wonder how qnd why would my camshaft be made 'improperly'? I own the bike since 2008 - it ran fine in all revs for sure till 2014 when I cleaned the carburetors and I probably have the issue since then (without having realized it since I never rev above 4000 when I am not on the highway). I will start now with checking airfilter then carbs and tank for anything stuck or even more likely water and if still no progress then proceeding to valve timing check.

Many thanks again
Tom

It still sounds like a valve timing issue to me. This would be from an improperly made camshaft. Ignition timing and carburation can be perfect, but if the valve timing is off, you will get what you are observing. You will need a degree wheel and observe when valves open and close. You will need a service manual to perform the valve timing checks.

 

[john zibell]

I hope John you are not right with this. Why would the engine then still rev up easily in neutral?
I also wonder how qnd why would my camshaft be made 'improperly'? I own the bike since 2008 - it ran fine in all revs for sure till 2014 when I cleaned the carburetors and I probably have the issue since then (without having realized it since I never rev above 4000 when I am not on the highway). I will start now with checking airfilter then carbs and tank for anything stuck or even more likely water and if still no progress then proceeding to valve timing check.

Many thanks again
Tom

You have just provided information that wasn't presented earlier. "I own the bike since 2008 - it ran fine in all revs for sure till 2014 when I cleaned the carburetors and I probably have the issue since then" What I described I have personally observed on a bike I owned. Valve timing was off by over 10 degrees on one cylinder. Mistakes in manufacturing happen. It displayed that trait since new. With no load it would turn to red line, but under load you would hit a wall and she wouldn't go any higher. Now you need to go over what you did to find the culprit.

 

[abbienormal]

I agree with John here. "Ran fine till I cleaned the carb". That means something is amiss with the carb cleaning. You had stated you had cleaned the carbs but it was not clear that was when the problem started.

 

[Tamas Jovanovics]

Apologies if I have been not clear about the carb cleaning. Of course I cleaned the carbs because I had some issues. I left the bike for a few months outside near the coast. I thought a cover is enough protection. It wasn't. I've never seen so much surface rost in my life. Luckily it came off with a good wash. But on top of all I forgot to empty the carbs before leaving the bike stand for those few months and the two circumstances together resulted in completely stuck carbs. The carb cleaning I thought went well because the bike starts and runs cold and warm fine. I just realized now that I have this rev issue above 4-5000 under load (but not in neutral). Indeed, most probably I shall have the issue since I cleaned the carbs. I will keep you updated. Many thanks again to all of you who contribute in the topic.

Tom

I agree with John here. "Ran fine till I cleaned the carb". That means something is amiss with the carb cleaning. You had stated you had cleaned the carbs but it was not clear that was when the problem started.

 

[jr1967]

Can you rotate the advance mechanism by hand? Another simple check to eliminate possibilities.

 

[Tamas Jovanovics]

Can you rotate the advance mechanism by hand? Another simple check to eliminate possibilities.

Not sure what you mean. What do you call 'advance mechanism' ? You mean the flywheel? The points? Apologoes for being an ignorant and thanks for clarifying.

Tom

 

[john zibell]

There are weights under the points plate and springs to hold them back. As RPM increases The weights swing out advancing the cam that actuates the points.

 

[jr1967]

Yes, it's a simple check: lift the back of the tank, take the cover of your ignition, (behind your right hand cylinder) and you'll see your contact points running on a central shaft. This shaft should be able to turn a few degrees against spring tension, with the above described mechanism that is hidden below your contact points. Just grab that shaft by hand and see if it can be rotated a bit. If not; there's your problem, make notes and take pictures, take it all apart, lube it and put it back together. If you can rotate it, you can check it off the list because the problem lays elsewhere. There should be a yellow bit of felt in the center of that shaft, put a couple of drops of gear oil on it, that will lube the cam on the shaft and the part of the contact points that run on it.
I hope this clarifies it a bit? No problem asking more questions, this is how we all learned. Plus studying the manual of course