76 SB, FI with a bucking issue

tswillow · Post by **tswillow** » Mon Jul 11, 2011 2:23 pm

We have a 76 SB that is 1 year plus into a restoration, engine is back in however it has developed a bucking problem after it is totally warmed up (10 to 15 miles of driving). The FI computer has been checked as well as the temp sensor, aux. air valve, air monitoring valve, spark plugs (and wires) points, condensor, coil, fuel pressure, We did replace the alternator as it was putting out 19 volts. Is it possilble the alternator putting out too much voltage damaged the fuel injectors? Any suggestions would be appreciated.

Gypsie · Post by **Gypsie** » Mon Jul 11, 2011 5:22 pm

Likely an obvious item but did you have a Vacuum leak hunt after full warmup? Maybe something is leaking once it is warm?

Checking the temp sensor included assuring securely seated? Does the SB have two temp sensors?

Fuel injectors damaged by overvoltage may be possible but further down on my list of maybes. Other electrical failures (points, coil, condensor) at full warmup are higher on the list.

Restoration? What is the condition of the fuel tank. Could it be that fuel flow is suffering interference. Not just pressure but flow rate.

Where you at? Come to the Lab if you can....

tswillow · Post by **tswillow** » Tue Jul 12, 2011 8:31 am

Have not looked for vacuum leak after warm up..is there a good technique for this?

All ingnitinon components have been checked or replaced (points, plugs, wiring, etc)

Temp sensor near cyclinder #4 is critical one, there is another near the alternator pully that is for cold starting only. Both appear are seated and working.

Fuel tank is new.

I had thought about the flow but don't know what it should be or how to check it.

We live in Plymouth, Wisconsin (eastern portion of the state, near Milwaukee)

Thanks for the input

RSorak 71Westy · Post by **RSorak 71Westy** » Tue Jul 12, 2011 9:17 am

Easy way to check for vacuum leaks is to spray something combustible like ether, at suspected leaks. If and when the engine sucks in the additional fuel, the idle speed will rise and or smooth out.

Post by **Amskeptic** » Tue Jul 12, 2011 9:24 am

tswillow wrote:We have a 76 SB that is 1 year plus into a restoration, engine is back in however it has developed a bucking problem after it is totally warmed up (10 to 15 miles of driving). The FI computer has been checked as well as the temp sensor, aux. air valve, air monitoring valve, spark plugs (and wires) points, condensor, coil, fuel pressure, We did replace the alternator as it was putting out 19 volts. Is it possilble the alternator putting out too much voltage damaged the fuel injectors? Any suggestions would be appreciated.

If the engine behaves cold, but misbehaves warm, see what the mixture is cold, and compare to what mixture is warm.

If richer cold .... richen it up for warm.
If leaner cold .... lean it out a bit for warm.
Yaah?
Colin

Gypsie · Post by **Gypsie** » Tue Jul 12, 2011 10:23 am

Amskeptic wrote:

If richer cold .... richen it up for warm.
If leaner cold .... lean it out a bit for warm.
Yaah?
Colin

I am interested in how this works.

Is this a similar procedure to the AFM adjustment sticky?
viewtopic.php?f=50&t=7761

Ether is found in what products? I have used gumout carb spray.

We found that a bucking issue reported for a type 4 turned out to be a lean condition. We richened it up (to the tune of 8 clicks ccw on the cog) and it appears at furst blush to have helped though it is still under observation.

steve74baywin · Post by **steve74baywin** » Tue Jul 12, 2011 10:28 am

Temp sensor 2 or vacuum leaks.

Itinerant Air-Cooled

Itinerant Air-Cooled

76 SB, FI with a bucking issue

76 SB, FI with a bucking issue

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