fuel distribution

[racer88]

I have put about a thousand miles on my 260 with 280 engine with 4screw round top su's since I got it on the road this fall. It seems to run great. I have been very carefull to make sure the float level is set correct sync'd both carb at idle and 2,000 rpm. Adjusted the nozzles 2.5 turns down then tweaked from there. I decided to check my plugs this morning and I found cyl. numbers 1,2,5,6 to be bone white cyl. 3 and 4 to be black and sooty. Cyl# 1&2 are connected by the same opening in the intake as viewed from the carb opening. The same goes for 5&6. #1 and 4 have their own runner. Has any one else noticed this condition with their plugs. Not sure if I have an issue somewhere else or is it a normal distribution problem with the su intakes. I tried to richen it up (bone white plugs are never good) but the car seems a little sluggish. Any ideas would be great

Thanks

Bob M

Edited October 15, 2010 by racer88

[Tony D]

Fix your vacuum leak by using a new intake manifold gasket and proper sealant.

 

On an aside, make sure the float level is correct and that you simply are not continually pouring fuel down the bottom of the manifold to 3 & 4 with a level making the gas run out the main jet continually.

 

You have mixture distribution issues, and outside of a bad float level deluging 3 & 4, improper manifold torquing and vacuum leaks would account for the rest.

[racer88]

Hi Tony

Thanks for the ideas. Sunday was tune the car day. I think I have found my distribution problem. When I first got the car on the road about a month ago it surge at a constant 3500 rpm in 4th gear. I searched some threads and determined that the float level was low as I had already tried to fix the surge by adjusting the nozzles up and down. I raised the float level bit by bit until the surge was gone. The car sounded great and ran strong at 3/4 throttle but when I opened it up it layed down, like it was running out of air. It turns out my fuel pump (electric) pressure was intermittently low (2psi)so raising the float compensated at idle made it to rich cruising and went bone lean at high speed. I corrected this issue added new plugs and they look great. I have read many of your post on fuel injection and you seem to have a good handle on injection. I have spent many hours on the dyno tuning holley carbs for late model stock cars but not much experience on su's. I am planning on converting my 260 to injection over the winter. I was thinking of machining up some adapters and mounting a couple of GM throttle body injection units on the su intakes with some sort of stand alone control system eg. mega squirt. Any thoughts on this idea would be great. many of the threads I have read on the induction debate Holley vs su or injection seem to be a few years old.

thanks

Bob

[Tony D]

SU TBI ADAPTERS???? You don't say? Like this?

 

 

Patton Machine, if you want to use the GMTBI Adaptors. Proven quantity, running in France on one car WITH GM ECU! Should be photos out there of them installed.

 

Adapter Page

 

Wonder Who Supplied the Hitachi Bodies as Prototypes?

 

 

YEAH, THIS ENGINE IS FUEL INJECTED!!!

 

 

Amazing what some tubing and routing of wires can achieve in the form of illusions, eh?

Edited October 19, 2010 by Tony D

[racer88]

I was actualy thinking of the complete gm throttle body assembly, but that looks pretty slick. Do you have to alter the carb body or can you change it back if you so desired. I would hate to render a good set of su carbs as un-usable. How close is the gm ecu in fuel requirements to what my L28 would need. This set up looks like just what I am looking for. If I decided to build a system like this would you be so kind as to steer me in the right direction as far as what injectors, ecu throttle position sensor etc.

Thanks

Bob

[Tony D]

Follow the links, they sell components and total systems.

Nothing you do to the carbs has to render them unuseable on Rick's conversion.

 

It's all pretty well explained on his website.

 

As for GMTBI injectors, don't have a clue, but generally most of the V8 stuff will supply more than enough fuel for anything we would produce N/A. The added plus is you don't need extreme high pressure fuel to run them!

 

Follow the links I gave and snoop around his site and FAQ's. The guy from France posts here, and posted his SU conversion when he had it installed. It's in a 240 and has been runing for over a year or so.

[racer88]

Thx Tony. It looks like that is the route I will be taking. I will post pic's and updates as the project moves along

Bob

Ps I wish the weather up here in Canada would turn crappy so I can stop driving the Z and start workin on her!

Edited October 20, 2010 by racer88

[Tony D]

You wish? Do you know what hell it is to live in Southern California? Every weekend a drive, a show, an event. A club meeting every week on Tuesday, Thursday, or Wednesday. Never raining so drive drive drive drive! You almost have to keep two Z's just so you can work on one because the other one is constantly driving almost 365 days a year.

 

I envy you guys who can take your car off the road for 6 months of the year and just work on it to get it nice. Man, I wish I had that luxury!

 

Crappy weather? What's that?

 

 

<EDIT> When you talk with Rick, tell him I sent you looking, and that I haven't forgotten the 52# of Datsun SU carbs I sent in a box for him to use as patterns to make adapters for EVERY Nissan with an SU from 1965 to 1978! (That includes JDM 38mm stuff!)

Edited October 20, 2010 by Tony D

[racer88]

Two cars Mmmmmmmm....... snow tires Mmmmmm........now theres a thought