MG MGB and MGB GT Tech Talk
The 1st picture shows both, the 2nd the front carb. I overstated the amount I guess, but piston still appears to be sitting too high. The 3rd picture is after I reverse the piston front to rear, seems more even. I also engaged the choke to full and the piston dropped down abit. Maybe not centered? The rest show the plugs (in oreder 1,2,3,4,) with about 5 miles on them after a good cleaning.
I would reroute the fuel line and move the filter. To much heat in the area you currently have them. $.02
Sorry, Is it idleing at normal RPM or really high. Do you have a meter to check the air flow.
Idle is good, using a flow meter the carbs will balance. Story goes, front carb is leaned all the way out and still rich, as noticed form the wet plug pics. The rear carb has some mixture adjust left and those plugs are closer to correct. The other issue (which may be the problem) is the forward piston is sitting high when at rest. If I reverse them, they seem to be more correct.
Also this a crossflow head so I don't have the heat issue as much as if it was sitting over the manifold.
Jimmy has forgotten 100x what I know about SUs, but I'll chime in anyway.
Seems like if pulling the choke causes the piston to drop, either the needle is hanging up in the jet, or the needle isn't seated properly in the piston or the top of the jet is above the height of the bridge (assuming that's even possible).
If you drop the pistons from an inch or so do they make a nice clunk when the reach the bottom of their travel?
Good Luck!
Paul
Brian,
You may have just named the clue. You said you pulled the choke and the piston dropped down to the bridge. The jets do have to be well centered for that to occur. Most of the Volvo HS6 carbs did have fixed jet needle setups.
As Paul said, most jets can be adjusted above the bridge. That is the other possiblilty with the same effects. Although pulling the choke should not affect the pistons at all.
Hey Paul,
Yes they are making the good clunk, thats why I didn't notice at first. If I pull the choke, the piston drops just a hair. Shouldn't drop at all so I must have an issue there. I think I'll try reversing the pistons and going with that. Between me and the PO we might have reversed them.
B..seein ya Wrote:
One of John Twist's YouTube videos is about matching pistons to dome. Basically he plugs the airholes in the pistons and with the pistons and domes removed from the carbs checks to see that they fall though their travel in roughly the same amount of time.
http://www.youtube.com/watch?v=IfU47Oqq9wA
Just watched the video and will attempt tomorrow. Need to figure out the correct needle before buying new one's. These are KN, so I think I should go to a leaner needle. Need to do some searching as these HS6's are Volvo 122's, I believe. So Jimmy are you saying these are centered correctly or need to be centered again?
Brian,
I think that Mac actually had the best advice. It is probably time to replace both the jets and the jet needles. When not correctly centered, both the needle and the jet, will be worn/scarred.
If it were me, I would probably start with SY needles as they were used in the "Special Tuning" setup HS6's. I really don't believe the KN needles have anything to do with the root of your problem. You should be able to balance, get a good idle, and run it around the block on any .100" jet needle. Beyond that would be getting it fine tuned.
Other likely needles to try (in order of my best guess):
SY - MGB Special Tuning HS6's
SM - TR3/4 H6's
TW - TR4A HS6's
KM - MGC
BAD - MGC biased needle
Jimmy is that something you might have or should I get in contact with Joe Curto for parts.
Thanks to everyone who had an input, appreciate the time. Message came from Joe.
Sounds like your jet is not centered, piston should be on the bridge
when car is off. Drop choke/jet and see if piston drops, also make sure
jet is a .100 hole in it not a .090
Joe
Jimmy, thanks again,
Brian
Brian,
Get them from Joe, that is where mine come from. Also, it is nearly the same cost to get a pair of complete kits as it is to get 2 jets and 2 needles.
I don't know much about anything, but it is obvious why BAD needles would be your last choice.