Engine stops pulling at 7k

[Guest]

Instead of continuing to bug Steve and Ed on this problem I thought I would throw it out to the masses and see if any have experienced something similar.

Been working on a 1980 750E with 5900 miles on it. The problem I am having is during exceloration at about 7000 rpms in any gear it stops pulling or feels the same as hitting a rev limiter on a modern day bike. Under 7k it runs like a champ, smooth as silk...

Here is the skinny..

5900 miles
Stock exhaust
Carbs cleaned and rebuilt with new stock mains and pilots
Stock airbox and new filter
New Battery
New plugs
New Petcock
POR 15 tank liner ( no rust, tank is clean )

[mlinder]

Stock airbox? Filter?

Checked for airleaks? Checked that timing is advancing?

[jwhelan65]

Stock airbox? Filter?

Checked for airleaks? Checked that timing is advancing?

Yes stock airbox with new filter..how do I check the timing?

[mlinder]

With a timing light.

Have you checked for airleaks?

[jwhelan65]

With a timing light.

Have you checked for airleaks?

Have not checked for air leaks...are we talking around the intakes?

[mlinder]

Yes, around the intake boots. From either side of the carbs.

If you haven't, spray carb cleaner around the carbs while it's running. RPM change? Air leak.

[posplayr]

Joe,
You need a timing light if you don't already have one. Timing will be about 14 degree at idle and by 2500 will be to 34 degree (check your manual).

Sounds like ignition, not sure why an intake leak would be an issue at 7K RPM.

Also what do your plugs look like? Hopefully normal............

Check voltage to the coils at 2500 RPM. You can have issues if the voltage is low (needs to be above at least 11 volts). Is it a hard start?

Jim

[mlinder]

Joe,
You need a timing light if you don't already have one. Timing will be about 14 degree at idle and by 2500 will be to 34 degree (check your manual).

Sounds like ignition, not sure why an intake leak would be an issue at 7K RPM.

Also what do your plugs look like? Hopefully normal............

Check voltage to the coils at 2500 RPM. You can have issues if the voltage is low (needs to be above at least 11 volts). Is it a hard start?

Jim

Because pulling air on more than one carb means too lean a mixture to keep pulling.

But, as I mentioned, it's probably the advance/timing.

Also, a reminder to him (you already know), the voltage you are checking for is on the ignition side of the coils, not the plug side

[jwhelan65]

Joe,
You need a timing light if you don't already have one. Timing will be about 14 degree at idle and by 2500 will be to 34 degree (check your manual).

Sounds like ignition, not sure why an intake leak would be an issue at 7K RPM.

Also what do your plugs look like? Hopefully normal............

Check voltage to the coils at 2500 RPM. You can have issues if the voltage is low (needs to be above at least 11 volts). Is it a hard start?

Jim

Hey Jim,

Yes it is very hard starting and the idle increases after it warms up. I had it out today and it killed, I had to turn the petcock to Prime to get it to start. Plugs are appear to be ok. Ed mentioned swapping out the igniter with my 1100 but the connection are different.

[posplayr]

Hey Jim,

Yes it is very hard starting and the idle increases after it warms up. I had it out today and it killed, I had to turn the petcock to Prime to get it to start. Plugs are appear to be ok. Ed mentioned swapping out the igniter with my 1100 but the connection are different.

I would say it is electrical in low coil voltage or bad ignitor.

My 1100ED gt progressively harder to start even though I had a new harness and left/right hand controls. Checked coil voltage and it was 10.5V and I had to use starter flid to get it to kick over cold.

With coi lrelay mod, fires immediately.

[posplayr]

Because pulling air on more than one carb means too lean a mixture to keep pulling.

But, as I mentioned, it's probably the advance/timing.

Also, a reminder to him (you already know), the voltage you are checking for is on the ignition side of the coils, not the plug side

I would have figured an intake leak would cause problems well before 7K RPM.

[hjfisk]

Hey Jim,

Yes it is very hard starting and the idle increases after it warms up. I had it out today and it killed, I had to turn the petcock to Prime to get it to start. Plugs are appear to be ok. Ed mentioned swapping out the igniter with my 1100 but the connection are different.

Are your floats adjusted high enough? it maybe running out of fuel when you start to get it wound up. The reason I ask you had to put it on prime to start after it died. also check that your fuel petcock is working properly. Try putting it in the prime position and take it for a ride and see if acts the same.

[jwhelan65]

Are your floats adjusted high enough? it maybe running out of fuel when you start to get it wound up. The reason I ask you had to put it on prime to start after it died. also check that your fuel petcock is working properly. Try putting it in the prime position and take it for a ride and see if acts the same.

I set the floats in the middle of the variance, but you maybe right it acts like a carb problem

[mlinder]

I would have figured an intake leak would cause problems well before 7K RPM.

It does. But pushing the air in front of you at 90mph is a lot harder than doing so at 40 mph.

It's an overall loss of power.

Not saying this is the issue. It's best to cover all the easy parts first, though, before you start getting into more complex testing/fixing.

[gearhead13]

I swapped ignitors from my '82 1100 to 750 no problem. Is the '80 750 a different plug setup?
I have both timing plate and ignitor here collecting dust if you need them.