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Discussion Starter · #1 ·
Hi everyone !

First of all, I'm new on this forum so hello again. My name is Alex, I have 24 and I have ridden old Moto Guzzi's for 3-4 y. I rebuild them with pleasure. I'm not one of the worst in mechanics but I still have a lot to learn.

I have a question for you guys about my '94 750 SS. I get to know her. Everything is original except two Bos "silencers". 38 000 km, no rust, clean, even the handles are original !
The only problem is that when I open the throttle (slowly or not), I don't have a linear acceleration, it's smoosly knocking but not always, sometimes it's fine but hardly never. It can be dangerous in a turn ! I always let it heat up and put two new NGK BR8EA-9 spark plugs but nothing change. Second thing, when I reach 150 km/h, she sometimes starts to run on 1 cylinder (I feel no power and remember when I had the same with a Moto Guzzi with deficient Motoplat ignition).

Do you guys think about a carburation problem (runs nicely on idle and rev also nicely in neutral) ? Ignition problem ? Coil problem ? I prefer to ask before disassemble everything !

Thanks, cheers,

Alex
 

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Hi everyone !

First of all, I'm new on this forum so hello again. My name is Alex, I have 24 and I have ridden old Moto Guzzi's for 3-4 y. I rebuild them with pleasure. I'm not one of the worst in mechanics but I still have a lot to learn.

I have a question for you guys about my '94 750 SS. I get to know her. Everything is original except two Bos "silencers". 38 000 km, no rust, clean, even the handles are original !
The only problem is that when I open the throttle (slowly or not), I don't have a linear acceleration, it's smoosly knocking but not always, sometimes it's fine but hardly never. It can be dangerous in a turn ! I always let it heat up and put two new NGK BR8EA-9 spark plugs but nothing change. Second thing, when I reach 150 km/h, she sometimes starts to run on 1 cylinder (I feel no power and remember when I had the same with a Moto Guzzi with deficient Motoplat ignition).

Do you guys think about a carburation problem (runs nicely on idle and rev also nicely in neutral) ? Ignition problem ? Coil problem ? I prefer to ask before disassemble everything !

Thanks, cheers,

Alex
Hi Alex,

Does your problem also appear while revving the engine at standstill, or only while riding?
Recently another member had issues where the gap of the spark plugs was not correct. Might be worth to check?
Are you sure the spark plug cables are ok? Maybe a somewhat loose connection or damaged cable?
Have you synchronized the carbs lately?

Good luck,

Helge
 

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Discussion Starter · #3 ·
Hi Alex,

Does your problem also appear while revving the engine at standstill, or only while riding?
Recently another member had issues where the gap of the spark plugs was not correct. Might be worth to check?
Are you sure the spark plug cables are ok? Maybe a somewhat loose connection or damaged cable?
Have you synchronized the carbs lately?

Good luck,

Helge
Hi Helge,

Thank you for your answer. It just appears while riding 'cause when I rev it standstill, it sounds really good ! I mean, mixture seems to be correct, no miss like too much air, good cold starts and good hot starts, nice torque (when runs good) and a nice chocolate spark plug color. I changed the two spark plugs just in case and the gap is ok.

I'll check the spark plugs cable and the sync. I ask because maybe the problem is known with those bikes ! Have you ever heard smth like that ? Maybe the ignition ?

Oh and, sorry for my english,

Thanks,

Alex
 

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When you have the problem what is the rpm?

BR plugs should not fit do you mean DR8ea-9?

ignition boxes if stock should not be a issue if you have aftermarket they are suspect.
open or closed airbox?
try swapping and see if it improves or worsens with more or less air.
 

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Discussion Starter · #5 ·
When you have the problem what is the rpm?

BR plugs should not fit do you mean DR8ea-9?

ignition boxes if stock should not be a issue if you have aftermarket they are suspect.
open or closed airbox?
try swapping and see if it improves or worsens with more or less air.
Oups yes sorry my mistake ! DPR8EA-9 !

It happens when I hit around 4500-6000 rpm ! I realize that that rubber above the airfilter with two holes is missing ! And the air filter is like the K&N DU-0900. So open airbox with kind of a perfomance filter I would say. Might be the problem. But I don't understand why it's happening when I ride, not standstill... 1st gear feels quite great, but the others no

It's the first time I have a such a "recent" motorcycle, sorry for the stupid questions !
 

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Make sure you’re getting good fuel pressure. There is a jet in the return line that has to be there to supply the carbs with enough fuel. The carbs probably need a rebuild if it hasn’t been done lately. Set the float levels when you do. There are lots of old posts to read but I will give one basic suggestion: Do a complete tune up , new belts, set valve clearances, make sure both plugs are firing well. Then, see how it’s ru after that. The mufflers and intake modifications are going to make it run lean, so you can either tune your carbs as is, or rebuild them and start fresh. Setting float level correctly might help the lean condition. You will probably want to buy a tuning kit for the carbs. I recommend Factory Pro but it’s your bike. But, first make sure you’re getting enough fuel, then figure out if it’s still lean.
 

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Go through the carbs, look closely at the needle/ needle jets. They are prone to wearing quickly and running excessively rich in the rpm range you describe. Also check the fuel filter, it's in the fuel tank and often neglected [out of sight, out of mind!] and they fill up with very fine rust particles.
 

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Discussion Starter · #8 ·
Thank you both for your ideas ! I will make sure the carbs run good and the fuel filter ! When the problem appeared, I tried to put the chocke on 'cause I though it might bean a lean mixture but I still had the bad feeling.

Here's a first on board with the gopro. You can feel it at 4:09 til 4:13 !

Well, I'll check everything ! Thanks and enjoy your weekend !
 

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the 750 is ok with the snorkles removed ime. they'll be a bit lean on the needles, but they have 140 mains std.
 

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Document the parts in the carbs when you go inside.
look for brand marks on components and if not sure take photos.

Remove the air filter and rev the engine (careful to not drop any thing in) watch that the slides are both opening.
In neutral with no load on the motor you may feel different results because
1. there is no load
2. there is no wind speed being forced into the motor.

Verify the vacuum chamber vent hoses are not where a side wind will lift the slides, you may have slides that are opening when the should not be if the lines are not routed properly.

What ignition boxes
what coils
what plug wires
what plug caps
 

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Discussion Starter · #12 ·
Document the parts in the carbs when you go inside.
look for brand marks on components and if not sure take photos.

Remove the air filter and rev the engine (careful to not drop any thing in) watch that the slides are both opening.
In neutral with no load on the motor you may feel different results because
1. there is no load
2. there is no wind speed being forced into the motor.

Verify the vacuum chamber vent hoses are not where a side wind will lift the slides, you may have slides that are opening when the should not be if the lines are not routed properly.

What ignition boxes
what coils
what plug wires
what plug caps
Ok thanks, I'll do that in the following days. When I'm in 4th or 5th gear, I can go full throttle and I feel hardly never the problem when I'm between 85-130 km/h, you think it's because I'm already in the wind so it isn't as forced as at low speed ?

I'll keep you in touch !

Alex
 

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Discussion Starter · #13 ·
Ok guys ! First, I check the needle. I put it higher (one before the last one). I think it's already better ! I'm gonna change the K&N filter (33-2566) with an original one ! I wanna see how it goes with the original parameters ;) During the winter, I will look closer inside but now, I need to ride it minimum 3 times/week !

Thanks for your recommandations !
 

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Discussion Starter · #14 ·
Update #2 : I badly tuned the needle. Now it's too rich. Spark plugs is too dark and the acceleration still need an adjustment. I bought a new original air filter. Maybe it needs a complete stage 2 carbs if I keep the empty bos exhausts, K&N filter so I will first try to run it good stock !
 

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Update #2 : I badly tuned the needle. Now it's too rich. Spark plugs is too dark and the acceleration still need an adjustment. I bought a new original air filter. Maybe it needs a complete stage 2 carbs if I keep the empty bos exhausts, K&N filter so I will first try to run it good stock !
Just out of curiosity, what altitude are you riding at primarily? I did not see this mentioned yet.
 

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Your needles and emulsion tubes probably need replacement. The hole tend to wear egg shaped and cause this problem. Factory Pro kits contain tit needles and nickel plated emulsion tubes to reduce wear.
 

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Discussion Starter · #19 ·
Hi AlexRoll, did you solved the problem with your 750SS ?
A little bit. I changed the needle setting (richer) and put the orignal air filter but still have problem at 2/4 of the throttle. I tried richer setting for the needles but was too much ! The main jet seems to be good. It's a shame that I can't cruise with little accelerations. There are not fluent.
Another strange problem : the 5th gear seems restricted ! I can't get faster than 130km/h. After that, it looks like running on one cylinder. So I have to get speed with th 4th gear ... Any ideas ?

I'm going on holiday to Italy next week, I'll knock on the door directly haha !
It's summer her in Belgium so I will work on a full upgrade in a few months, during the winter...

Thanks !
 
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