MG MGB and MGB GT Tech Talk
I think i desperatly need some advice here... installed my rebuilt H1F4 carbs runs smooth but at 2500 rpm adjustment screws are all the way loose but cant get rpm to drop. if i tighten the jet adjustment screw rpm goes even higher if loose by 5 turns it drops but runs rough and stalls.
Help...
Vacuum leak somewhere because of a rubber hose split or something like that?
Vacuum leak??? Did you spray around with carb cleaner to hear for one?
there are a lot of different things that could be wrong.
Are the throttles actually closing? Is the piston free and coming down properly. spring/dashpot oil? Vac leak at throttle shaft (how did you handle the throttle shaft when you "rebuilt" them?). Vac leak at carb mount points or elsewhere? Fast idle screw wrong? Mixture way off? Cable not adjusted properly? Jet assembly installed improperly? float level too high? Timing? vac advance line off or not plugged?
etc.
you kinda need to go to square 1 and check everything until you find and fix it.
I had a similar problem when I first installed my HIFs. I had also just rebuilt them. For me, it turned out that I haden't taken care to make sure that the throttle plates were correctly centered and thus closed properly. Take them off and and hold them up to the light. You should see very little (or none, preferably) light seeping in from around the trottle plates. I loosened them up and carefully adjusted them until there was barely any light seeping through. Now they run proper.
Also, if your plates have the spring valves in them, make sure the springs are good and closing completely - otherwise, I suggest getting a set of early plates without the valves - just remember to center them when you install.
There are other things that can cause it to idle too high (vac leaks, timing, mixture), but if the screws are all the way out, then throttle plates should be closed and no gas should be getting in. If the plates are sealing good, and the screw is all the way out, I can't imagine the car would be idling very high - if at all. Check those plates.
I suspect the plates but i will do a double check for a vacum hose i may have unpluged by mistake.
Thanks to all
loosend all the linkege loosend all the cables so the carbs would be on there own.
ajusted the mixture screw until the jet came even with the platform and then gave them one full turn clockwise, unscrewed the throtel and high speed screws so there is no contact. turned the engine over and she started up and held steady at 2000rpm.
i think maybe i did something wrong during reasembly...going home in a GMC safary tonight and back to the drawing board tomorow.
I am thinking did i or did i not put that little spacer/ washer under the jet it's called a " washer-sealing page 123 # 20 in the VB catalogue. or maybe the metering needle is to high could that cause high idle?
Again thanks for your input
Nick
something very simple but i had a similar problem, and i replaced the throttle return springs and everything is now perfect
Ken
I think Jake Scaltreto nailed it dead on, the throtle plates or butterflys have a lot of light comming trough especialy one of the two.
To the point as the engine was running i could push one of the piston in the carb down
by 3/16" with my finger and it would drop the rpm.