100kph 6k stumble
 

I have been reading lots of hesitation and stumble related threads but most I see are stock(ish) cars. And I would just feel better with more direct advice/ideas in relation to my own cars set up

I have an 83 GSL with a street ported SA engine (68k on the rebuild)
Clean rebuilt carb (500kms)
No rats nest
RB header (68k) with single muffler (50kms)
Performance coils (68k)

Over the last couple days I have developed a stumble like its being starved of fuel.

It seems when I am in 4th or 5th gear and doing upwards of 100kph and ask the car for more power up and over 6000rpm it starts to sputter out.


3000 - 7000 is my power range so for me my car might as well be the family sedan atm.


I just came from the parts store with a new fuel filter and I have another pump I can install already just want to see if other agree that's where I should be looking first, or?

I think your on the right track. Change the filter and then do a flow test
of your current pump and make sure its flowing about 1 gal a minute or so, even
3/4 gallon in a minute means your pump is at least flowing well. Do this by
disconnecting the line at the carb and running it into a bucket.

Under load like that, if it still persists, I would check to make sure all your
grounds are good and that your getting good power out of your alternator. Make
sure its not a slipping belt. At those rpms a slipping belt might rob your alternator
of power and result in a lower voltage at the pump. Note I didn't say replace the
pump yet. If it was working fine with this setup and just started acting up it could
be one of these simple things and you don't need a new pump.

You didn't say what kind of pump your running or what you bought but a stock
pump may have problems keeping up with your setup if its not in good shape.
Even then a new stock pump might have issues as well.

Are you using a relay setup on your current pump installation right now?
Sometimes that can really help as well with the how old the wiring loom is.

Thank you very much, that's extremely helpful information.

It is running a stock fuel pump set up. (I have a 6psi carter and holly regulator I could run if needs be)

Could you explain a relay set up in regards to the pump for me please (wiring is not something I understand easily)

I did recently run into a problem with my charging system (new alternator on order for Monday) so that actually makes sense now that you point it out.

Whats your carb setup? I hope its a modified nikki and not just stock. Either way the
stock pump won't keep up. You'll want to put that carter on and use the holley reg to
keep the pressure down around 2.5 psi.

Sounds like the weakened alternator initially caused your issues.

Putting a relay in is as simple as runing a hot, non-switched lead from the positive battery
connection to a relay for the pump and using the stock relay power wire to signal the
relay to switch the power to the pump. I put mine right under the bin area behind the drivers
seat and it was real easy to hook up. I'm sure if you search you can find someone has a
picture up of what the wiring looks like.

The nikki appears to be modified (but sorry I don't know much about it) Thanks for the advice about changing the pump I had thought about swapping it out as it were..

I found the problem with the charging system and fixed it but came up with a new issue https://www.rx7club.com/showthread.p...8#post11004578

Excuse my ignorance here but I guess what I don't know/understand is whats the relay for? I ran the carter in one of my jeeps and just went from 12v - toggle - pump