Losing Revs on highway

[Stoffregen Motorsports]

I've seen other castings with the numbers cast up front. It was an era thing, the earlier the head, the more likely it's up front.

 

I could be wrong of course...

[Kyokutou]

Is there a fuel pressure gauge  ? Mikunis are sensitive to fuel pressure.Also pull the jet covers off and check for loose jets.I have to check the jets on mine constantly.I know when they're loose,it starts coughing and running rough.

 

Checked the jets this morning.  On the front carb one of the jets was so far out it looked like it was touching the cover.  On the rear carb one jet was touching the cover the other jet was half way out.   I tightened up the jets and the car ran real good today.

 

I will keep everyone updated if this fixes the issue.

 

Thanks Again

[banzai510(hainz)]

10min fix

I told you!!!!!!!!!!

 

I keep a screw driver just for this.

 

also the inner venturi can become loose. This will also give a high speed cut out. It will wiggle around

[Stoffregen Motorsports]

The auxilliary venturi (inner venturi) can be shimmed with a strip or two of beer can.

[Kyokutou]

10min fix

I told you!!!!!!!!!!

 

I keep a screw driver just for this.

 

also the inner venturi can become loose. This will also give a high speed cut out. It will wiggle around

 

 

I'll look into the inner venturi next.  So can I tighten the inner venturi the same way I was able to tighten the jets?  or do I need to remove/replace

 

Quick update on how the car's been running.   After 20-30min on the highway at speed 60-70mph  the car will still lose revs until it stalls out.  If i'm in stop and go traffic or driving around town it runs fine.  Also when I'm in gear but off throttle i'm popping and backfiring when i'm in neutral the backfiring goes away.

 

Thanks again for all the help 

[Doctor510]

I'll look into the inner venturi next.  So can I tighten the inner venturi the same way I was able to tighten the jets?  or do I need to remove/replace

 

Quick update on how the car's been running.   After 20-30min on the highway at speed 60-70mph  the car will still lose revs until it stalls out.  If i'm in stop and go traffic or driving around town it runs fine.  Also when I'm in gear but off throttle i'm popping and backfiring when i'm in neutral the backfiring goes away.

 

Thanks again for all the help 

 

Are they 40's?  Venturies, both the inner and the outer are held in place with a set screw and lock nut,SLIGHTLY loosen the lock nut and tighten the set screw, you don't have to be the Hulk when you do this, just tight, using a screw driver, hold the set screw and tighten the lock nut.  If they are Weber's all bets are off.

[Kyokutou]

 

I'll look into the inner venturi next.  So can I tighten the inner venturi the same way I was able to tighten the jets?  or do I need to remove/replace

 

Quick update on how the car's been running.   After 20-30min on the highway at speed 60-70mph  the car will still lose revs until it stalls out.  If i'm in stop and go traffic or driving around town it runs fine.  Also when I'm in gear but off throttle i'm popping and backfiring when i'm in neutral the backfiring goes away.

 

Thanks again for all the help 

 

Are they 40's?  Venturies, both the inner and the outer are held in place with a set screw and lock nut,SLIGHTLY loosen the lock nut and tighten the set screw, you don't have to be the Hulk when you do this, just tight, using a screw driver, hold the set screw and tighten the lock nut.  If they are Weber's all bets are off.

 

 

 

They are Mikuni's.  I'll give it a try tomorrow and let you know.  Thanks for the quick response

[banzai510(hainz)]

YOu dont have to tighten the venturi if its not loose. Stick finger in there and feel if it wiggles..

All this shit is like POP metal and strips out ez so be careful.

 

If there is a pertrnix ignition then see if the ballast resisitor still installed.

Take photos of the coil area and the wiringThen maybe coil is getting HOT. if not ballast and still stock coil?

[Kyokutou]

YOu dont have to tighten the venturi if its not loose. Stick finger in there and feel if it wiggles..

All this shit is like POP metal and strips out ez so be careful.

 

If there is a pertrnix ignition then see if the ballast resisitor still installed.

Take photos of the coil area and the wiringThen maybe coil is getting HOT. if not ballast and still stock coil?

 

Thanks for the warning.  They were all pretty tight.  1 of the 4 I got maybe a 1/3-1/4 turn on the other 3 they hardly moved.   

 

It does have a pertrnix ignition setup.   My first post has a youtube link it shows the setup pretty good.  I can take additional pic's if it'll help.

 

Thanks again

[banzai510(hainz)]

Spund like you need a valve lash adjust but it hard eith vid as it always amplifies the odd weird noise.

 

The ballast resistor look like a 3 pole type that is on Z cars. I really dont know how or why they are that way.

I see you have a Pertronix coil. Be nice to find out the ohm value on this as if its a 3 ohm one then going to the ballst is not needed as your adding to many ohms. But I see its using the middle post and the end one. so I dont know what this does.. Datzenmike or others might know what it is. So maybe when you go faster its loosing soem power to it.

 

The + side of the Pertronix will go to the blk wht wire that goes in to the ballast. this is the FULL 12/14 volts. this is what you want. .

 

Thats my next best guess unless you can get a timming light on there and give us that infor. Maybe dist is slightly out of time on top end or soemthing but my experience I had good luck with all distrubutors stock or SSS type and they run fine unteill they just wear out