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Question about adjusting individual injector flow on fuel distributor

Hey guys,

I have a question regarding adjusting individual fuel injector flow on the fuel distributor of my '87 930. I have read the threads on flow testing the injectors including to be super careful making small adjustments on the fuel distributor itself!

My question is in the pic below is that allen screw cap the actual flow adjustment for that cylinder? Or do I need to remove that cap and the actual allen screw for flow adjustment is located under the cap?

Thank you for the help!

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'87 911 turbo, '10 Cayman S
In the past - '71 T, '77 S 3.6, '80 SC, '88 3.6 cab
Old 03-18-2014, 08:17 AM
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CIS fuel distrib. individual fuel line adjustment HELP..Fixed? - Rennlist Discussion Forums
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1987 GP White 930
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Old 03-18-2014, 08:53 AM
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The actual allen head spring tension differential pressure adjustment for flow adjustment to that injector is under that allen head button head screw
Unscrew it you'll see it under there. If it's rusty put some spray lube on it first.

The button head cover is 4mm allen head and the flow adjuster is 3mm allen head if I remember correctly. Either way use the metric allen head wrench that fits right.

Small adjustments to the adjuster allen head make a noticable difference so go slow with patience..

good luck!

edit: I forgot to mention turning the allen head flow adjuster clockwise increases spring pressure pushing the diaphram that seperates the upper and lower chambers in the fuel head downward away from the metering orifice above it increasing flow to that injector. And of course turning it counterclockwise lowers spring tension allowing lower chamber differential (system) pressure to push the diaphram upwards against the orifice which lessens flow to that injector.

It's kind of like a small final fuel pressure regulator to fine tune the amount of flow going to each individual injector.

Last edited by JFairman; 03-18-2014 at 09:11 AM..
Old 03-18-2014, 08:55 AM
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Thanks guys. I really appreciate the info.

Basically what I've got going on is cylinders 2 and 5 are running leaner (hotter?) than the rest. Cylinder 2 especially. I've currently got the engine out for maintenance and while I'm in there I'm putting new fuel injectors in (JFairman I know I know I should just clean the ones I have!) then I'll flow test the new injectors.

After I have the car back together and running I plan to also use an infrared thermometer on the header pipes to check their temps in relation to each other, then adjust as necessary. I'm hoping I can richen #2 and #5 a wee bit to balance out exhaust temps.

It's probably worth mentioning that I am going from B&B headers to RarlyL8 equal length headers so I'm also wondering if the equal length pipes will affect exhaust temp balance between the cylinders. Unfortunately I didn't do a 'before' test with my original fuel injectors and B&B headers.

One thing is for sure --- I'm looking forward to getting the car back together to go driving/tuning! It's been a loooong winter...
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'87 911 turbo, '10 Cayman S
In the past - '71 T, '77 S 3.6, '80 SC, '88 3.6 cab
Old 03-18-2014, 09:29 AM
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Here are a few interesting comments from the Rennlist link above:

"The little Allen screws underneath the caps are needle-and-seat valves. Turning in will reduce the amount of fuel going to that pot, and also raise the pressure going into the other pots (a double-edged sword). Backing the needles out increases the flow to this pot, and lowers the pressure to the other pots. Be careful!"


"I read what he said as being -- adjusting any of the screws affects them ALL to some degree - the more you open one port, the less there is for the others, and vice versa. Think of it as a garden sprinkler with 8 outlets - block one, the other 7 get more; open one up, the less all the others get. Once you play with one, ALL will need some adjustment."

That last sentence is especially interesting. From what he is saying if I richen up #2 then at the same time I'll be very slightly leaning out 1, 3, 4, 5, and 6!
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'87 911 turbo, '10 Cayman S
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Old 03-18-2014, 09:39 AM
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Did u buy rebuilt injectors ($55) or new ($175)?
Old 03-18-2014, 11:57 AM
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Quote:
Originally Posted by S1000RR View Post
Did u buy rebuilt injectors ($55) or new ($175)?
I'm in the process of buying new (but discounted) euro injectors.
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'87 911 turbo, '10 Cayman S
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Old 03-18-2014, 02:42 PM
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Quote:
"The little Allen screws underneath the caps are needle-and-seat valves. Turning in will reduce the amount of fuel going to that pot, and also raise the pressure going into the other pots (a double-edged sword). Backing the needles out increases the flow to this pot, and lowers the pressure to the other pots. Be careful!"
From what i have read here and from what JFairman just posted clockwise richens and counter clockwise leans on our fuel heads. Turning in to me sounds like clockwise, is the above statement wrong?
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Old 03-18-2014, 03:00 PM
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Quote:
Originally Posted by oilonly View Post
From what i have read here and from what JFairman just posted clockwise richens and counter clockwise leans on our fuel heads. Turning in to me sounds like clockwise, is the above statement wrong?
Yes I think it is wrong. I'm sticking with JFairman's description of leaning/richening.

I mostly posted the 2 quotes from the Rennlist link to mention the idea of making an adjustment to one cylinder slightly affects all the other cylinders.
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'87 911 turbo, '10 Cayman S
In the past - '71 T, '77 S 3.6, '80 SC, '88 3.6 cab
Old 03-18-2014, 03:06 PM
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