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Help with SU's[1800/69] posted by angelo on
Wednesday, 30 June 1999, at 9:25 a.m.
Hello all, and thanks in advance for any help. My wife's 1800 runs well except for one point in the rpm range. The tach is wildly optimistic, so lets just say that at 3000 or so the engine vibrates. You can feel it on the accelerator and shift knob. Above or below this rpm range, everything is well. While standing at the engine, I saw gas squirting out of the overflow vents (the small hole right at the intake hoses) at this rpm only. Again above or below - ok. Sound familiar? Is the vibration caused by the carbs or are they spitting because of the vibration? BTW the plugs are tan (maybe a little dark) and the engine mounts look good. The vibration occurs in gear and in neutral.
Thanks.
Gas Tank update...clean and good
Oil Sludge update...Took the advice of several HOT oil changes at 200 mile intervals. Looks a lot better now. If I see ANY sludge again, I'll try a quart of ATF. Thanks for the help guys.
Angelo '90 240/ '98 S70/ wife's '69 1800/needs a lot
Re: Help with SU's[1800/69] posted by Chris Mullet on
Wednesday, 30 June 1999, at 11:42 a.m.
Either a worn viscos fan clutch or timing gear can cause a rattling sort of racket at certain RPMs.
--Chris
Re: Help with SU's[1800/69] posted by Terry Geiger on
Wednesday, 30 June 1999, at 12:31 p.m.
I've seen this with SU's on Triumphs. What is happening is when the engine reaches a certain rpm, it causes a vibration that causes the floats to rapidly "bounce" in the float bowl. Everytime the float bounces, a small amount of fuel is allow to enter the fuel bowl, even though the fuel bowl is already full, causing the fuel bowl to overfill and overflow (that why you're seeing fuel from the overflow tubes). This is especially true if you have intalled grose ?(sp) jets in the carbs.
A friend of mine autocross a '69 Triumph Spitefire with dual SU's and we found this was the case. We swapped the grose jets for conventional needle and seat configuration and the problem was solved.
While on this subject, I need some SU HS6 carbs with 1.75 inch bore. They would have come on a B18D engine. If someone has a set they'd be willing to part with please let me know.
--
Terry - 1986 240 DL 219,000 miles and counting
Re: Help with SU's[1800/69] posted by Bob Mayer on
Thursday, 1 July 1999, at 9:29 a.m.
Angelo:
I recently had a very similiar problem with my 122 only the vibration/leaking occurred at idle. I tried grose (gross) jets but that made the problem worse. The engine was in good tune and ran excellently other than that. I tried fitting the float valves a little lower in the float chamber by using one washer that I received with the grose jets. That improved the situation, but didn't cure it. I cured the problem by... are you ready for this?... replacing the motor mounts. I don't know why they were in such poor shape. After all, they were only 33 years old! One of them was broken in two. Replacing the motor mounts limited the engine's movement which made the problem that Terry described go away. I hope this helps you. Good luck.
Bob Mayer, '66 122S, '71 R75/5