1996 sport 1100 carb idle

[ajonen]

I am still working to get this 1996 Guzzi Sport 1100 carb to run at its best. So far I have:

 

1. installed a new digiplex 402 cdi. Since the guzzi only needs the timing it seems to work. It has rectified many of the timing problems I was experiencing.

 

2. The previous owner had installed mikuni 38 flatslide carbs in an effort to fix the problem previously. Aftermarket pipes were also installed.

I have the mikunis running very well at top, mid and off idlewith a 170 main jet, needle on middle clip, 17.5 pilot, pilot/air screw turned out 1.5 turns. I am also getting about 40 MPG.

 

The problem I am experiencing is that it won't idle consistently. It will idle from startup at 800 - 900 rpm just fine. When I drive around a bit and then stop it will idle for a bit then die. It spits out the carbs when it dies. If I turn the pilot/air screw out more it spits/pops out the carbs more.

I am thinking it has something to do with the vacuum hose going from the intake to the cdi or something with the spark failing at idle. The bike runs perfect at every other throttle level.

There was only one vacuum going from the left side intake to the digiplex unit. The other intake was capped off. Should both intakes be connected with a T and then go to the digiplex? I am thinking that at low idle the digiplex is getting confused b/c it doesn't have consistent vacuum from the alternating piston firing. Any thoughts?

[ajonen]

I just found a guzzi 1100 carb manual. Looks like the vacuum should be T connected into the digiplex:

[Skeeve]

There was only one vacuum going from the left side intake to the digiplex unit. The other intake was capped off. Should both intakes be connected with a T and then go to the digiplex? I am thinking that at low idle the digiplex is getting confused b/c it doesn't have consistent vacuum from the alternating piston firing. Any thoughts?

 

You answered your own question vis a vis T-ing the vacuum line. If that doesn't cure it, you might want to check if the cam chain tensioner is up to snuff: iirc, similar symptoms were reportedly cured in the past by another v11lm member who found that his idle was jumping all over the place due to slack in the cam chain. Easiest way to do this would be to hook up a strobe light and check the idle timing: if the timing is jumping all over, then it's likely due to this cause, as the different cylinders get varying fuel charges from the cam alternately opening late or on time...

[ajonen]

well the vacuum hose T didn't fix the idle.

I also tried to lower the float level. Didn't fix the idle either.

I am going to try and replace the O-ring on the needle as it seems to be dripping gas a little out of the carbs.

 

I am a newb so I posted a topic on how to check the timing.

Thanks for the help.

[ajonen]

I also just noticed on the mikuni's that the overflow tube was connected to one of the vents. It has gas in it too! I disconnected the overflow from the vent so that it could actually drip the gas instead of filling the carb. We will see if that helps.

[docc]

Hi, Ajonen,

 

Apologies, but I thought we could address your timing question in this thread without a separate one.

 

There is a rubber plug on the right side of the bell housing used to see the top-dead-center marks for valve adjustment ("D" for right and "S" for left). I don't think the flywheel has any actual timing marks. You may be able to make a mark, visible with a timing light, that would tell you if the timing is jumping around indicating a bad cam chain tensioner.

 

Otherwise, there are some simple things to try first:

 

-set your valves to "world spec" (0.006" intake/ 0.008" exhaust) *apologies for quoting "world spec" in inches, but I see you are in SoCal/USA*

 

-Increase your idle to 1200-1500 rpm. Some of the tachs read 300-500 rpm low and no well cammed Guzzi likes a low idle.

 

-Balance your throttle linkage very carefully. The fluid devices (like Mercury sticks) are more effective than the electronic devices (like "TwinMax")

 

-be certain your air filter is clean and up to service and there are no air or exhaust leaks.

 

 

Certainly some of these motors have suffered from needing valve and guide service, but let's try the simple stuff first!

[Skeeve]

Certainly some of these motors have suffered from needing valve and guide service, but let's try the simple stuff first!

 

K.I.S.S., indeed!

 

Isn't that the Guzzista mantra & why we ride these antediluvian beasts in the 1st place?

[ajonen]

So I just adjusted the tappets and the left side was WAY too tight. Now the left side is VERY loud. Is this something I should worry about.

[gstallons]

Take the cover back off & check your work.

[Tom M]

So I just adjusted the tappets and the left side was WAY too tight. Now the left side is VERY loud. Is this something I should worry about.

 

Yup. You probably checked and adjusted at TDC on the exhaust stroke instead of the compression stroke. That would explain why they were so tight when you checked them. This time start looking for TDC just after the intake valve closes as you're turning the engine over.

[ajonen]

So I just adjusted the tappets and the left side was WAY too tight. Now the left side is VERY loud. Is this something I should worry about.

 

Yup. You probably checked and adjusted at TDC on the exhaust stroke instead of the compression stroke. That would explain why they were so tight when you checked them. This time start looking for TDC just after the intake valve closes as you're turning the engine over.

 

 

Yup that is exactly what I did. Fixed now.

Well I synced the carbs best I could by hand.

I set the tappets correctly.

Still having idle trouble.

 

I am going to try and set the float level and replace the o ring on the needle float bowl.

The bike drips gas when it is sitting so this IS a problem that I CAN solve. One less variable to have to deal with.

The bike may be "loading" up due to a faulty o ring or needle or brass needle float bowl.

One problem at a time you know.

[Orange Guzzi]

The cure I found for the popping and hiccuping was easy, but not long lived. I found that if i synchronized the carbs with the idle screws the problem went away. Also I sychronized the the carbs with the throttle pull cables.

 

What made the hiccup come back was when I was at a stop light and turned the idle screws out of sync. Also make sure you keep the idle at 1050-1150 rpm. The bike will idle at a lower rpm, less than 1000, but needs to be at the higher spec'd rpm.

 

MY sport work best with the clutch engaged and rolling down the road. Yee ha.

[ajonen]

Finally got it running.

here is the full run down.

 

1. cdi unit was dead. Replaced with a cdi unit from a ducati. It only needs timing so it worked fine. ( Saved about $900 by finding out this gem of knowledge.)

2. carb boots were not tightly sealing. replaced with new sport carb boots.

3. carb overflow hoses were not draining. rerouted correctly.

4. float needles were not seating. replaced oring on needle float bowl. adjusted floats until carbs stopped draining gas.

This fixed the horrible idle.

5. added vent hose to cdi to both intake boots.

6. synced carbs for idle and slide.

7. mikuni flatslide 38 with KN filter and HP exhaust.

17.5 pilot

1 turn out pilot screw

170 main

needle on middle clip.

idle set at 1000 rpm.

 

Big lesson here is don't trust the mikuni factory float levels. The pressure of the fuel was pushing the needles open.

[Fritz]

Hum? My 96 Sport with the OEM delortos had the same idel problem. It turned out to be not enough cable slack. I run about an extra 1/16" and alls well.