john g Posted March 18, 2012 Share Posted March 18, 2012 Driving the 7 last weekend and after about 30 minutes the car developed a misfire when accelerating and progressively got worse, even more so when accelerating hard. I managed to get home by gently feathering the throttle – to avoid the misfire. I removed the top of the weber twin 40’s and removed and cleaned the jets to ensure there were no blockages, I cleaned the check valves end checked the floats – all seemed OK, I then balanced the carbs. Took the car out today and again after about 30 minutes the same problem occurred. Has anyone any ideas 🤔 Link to comment Share on other sites More sharing options...
Gordon C Posted March 18, 2012 Share Posted March 18, 2012 i would start by looking at your ignition leads. Make sure you have a good spark at the plugs. Might be one of the leads is breaking down once it gets a little warm. When did you last change the leads ? Link to comment Share on other sites More sharing options...
John Hughes Posted March 18, 2012 Share Posted March 18, 2012 If you have a mechanical fuel pump it could be that. Had a similar problem with my old car would missfire if running above 60mph for a few mins or when I accellorated hard. Was due to the mixture going weak due to a tired fuel pump. I changed all the plugs, leads, dizzy cap etc before changing the fuel pump. Edited by - John Hughes on 18 Mar 2012 22:10:15 Link to comment Share on other sites More sharing options...
CHRIS TODD Posted March 18, 2012 Share Posted March 18, 2012 I have had a similar problem and found that a new set of plugs to be the cure. I seem to go through plugs every 1500 miles, but cheap to fix 1600 xflow, twin 40's too Link to comment Share on other sites More sharing options...
James_Russell Posted March 18, 2012 Share Posted March 18, 2012 Sounds like Plugs/HT leads to me. Link to comment Share on other sites More sharing options...
andy_h Posted March 18, 2012 Share Posted March 18, 2012 Have you worked on the ignition coil, I.e are the wires (power) connected the correct way around. Don't ask me how I know this little gem 😳 Link to comment Share on other sites More sharing options...
Roger King Posted March 19, 2012 Share Posted March 19, 2012 If you're running cleanly on light throttle, but misfiring on big throttle openings, there's a chance that one of your Auxillary Venturis has moved, which stops the main jet from supplying fuel while not affecting the slow run jets. Check to make sure that all the locking screws are still in place under the barrel of each carb. And look down the barrels to see if one of the AV's has rotated relative to the others. Link to comment Share on other sites More sharing options...
Area Representative paul richards Posted March 19, 2012 Area Representative Share Posted March 19, 2012 John If it runs fine and then gets gradually worse, especially on full throttle, then I'm with John Hughes and recommend looking at the fuel pump. Unfortunately a tired fuel pump can't keep up with webers. Good Luck. Link to comment Share on other sites More sharing options...
Paul Deslandes Posted March 19, 2012 Share Posted March 19, 2012 Probably a long shot and unlikely if this is a recent phenomenon but check that air can get into the tank to replace the fuel that's been used. When you've driven far enough to get the problem, stop and hop out ( 😬) and undo the filler cap. If its hard to get off because of a vacuum or you get a a whoosh of air going in, that's your problem. This might occur if you've recently changed your filler cap or the breather's blocked. A small hole drilled through the cap will solve the issue. Link to comment Share on other sites More sharing options...
Molecular--Bob Posted March 19, 2012 Share Posted March 19, 2012 Mine did something similar when the locking collar on the distributor came loose, it would run ok cold but as it warmed up it just refused to run clean. Checked all of the above before the local backstreet mechanic sorted it for me. Link to comment Share on other sites More sharing options...
Brian Soper Posted March 19, 2012 Share Posted March 19, 2012 I have had encountered similar problems on my S2 A series engine in the last 32 years !!!! , first time it was the distributer cap and the second time it was spark plug lead caps. The latest dist caps are not as good as the old ones and even if they look perfect they will track and cause missfire , if you use copper HT leads then fit NGK plug caps most repro ones are rubbish , you can get Champion ones from SVC sometimes Brian Link to comment Share on other sites More sharing options...
Neil66 Posted March 19, 2012 Share Posted March 19, 2012 Can I just say, these are the threads that are worth their weight in gold on BC - getting hold of folks experience & transferring that to others is so valuable. We try to do this in the industry I work in and it's very hard to do.. I don't mean this as a hijack and I certainly don't want to dilute the topic with further discussion on this - so please don't reply but keep the experience coming ;-) Link to comment Share on other sites More sharing options...
Roger King Posted March 19, 2012 Share Posted March 19, 2012 Can't help thinking in retrospect that Paul Deslandes may have a point with his post (above) Link to comment Share on other sites More sharing options...
john g Posted March 20, 2012 Author Share Posted March 20, 2012 Thank you for your inputs . Will keep the thread updated. Link to comment Share on other sites More sharing options...
kenny. Posted March 20, 2012 Share Posted March 20, 2012 Hiya John, that little black x/flow of mine did exactly the same if you remember. I went all around the houses then changed the plugs..........doh!!!......sorted. By the way I'm not working today and am in the house so if you need a lift then give us a bell Edited by - kenny. on 20 Mar 2012 13:17:47 Link to comment Share on other sites More sharing options...
John Hughes Posted March 20, 2012 Share Posted March 20, 2012 John I have a collection of Crossflow bits including a brand new Bosch coil, Lucas / Aldon dizzy cap / rotor arm. Will check what else. You are welcome to try them if you want. Symptoms do sound awfully like my problems when in the IOM 2yrs ago though Link to comment Share on other sites More sharing options...
eric Posted March 20, 2012 Share Posted March 20, 2012 I have just experienced misfires, I changed the spark plugs but same problem. A new distributor cures the pb, I think it was due to a damaged cap. If it can help. Link to comment Share on other sites More sharing options...
john g Posted March 20, 2012 Author Share Posted March 20, 2012 Chris & Kenny - plugs only covered about 2000 miles, however worth considering as Chris says, cheap. John - I'll see how I go on and may take up your kind offer. Paul - now you mention it, years ago I had a similar problem with my 1965 850 mini. Will try it. Roger - all lockscrews and AV's are OK. Andy - new coil and all OK. Bob - dizzy seems OK. Had a new petrol pump in the garage and fitted it tonight. Obviously need to try it now. Eric, Brian, James - If (when) problem still exists will check the spark at each plug or even just buy new plugs, leads and cap. Once again thanks for everyones inputs. Link to comment Share on other sites More sharing options...
virden Posted March 21, 2012 Share Posted March 21, 2012 JOHN, I suffered precisely the same problem with my Xflow after I renewed things. It would start well, run well for about ten miles then develop an increasing reluctance to rev, until it died. If left to cool down for 20 mins, it would start off and repeat the cycle. In the end I found the new coil didn't work in my set set up. Changed back to the old one, and have never looked back. Perhaps it was the wrong coil or simply faulty, I don't know. Good luck Link to comment Share on other sites More sharing options...
john g Posted March 24, 2012 Author Share Posted March 24, 2012 OK chaps, update. Installed a new fuel pump and went for a drive yesterday all seemed OK, super to be honest! and then - misfire again . This morning new NGK BP7SE's, to replace last years NGK BP7SE's and yeah problem sorted . So, thanks for everyones help and Neil, yes BC is super 😬. Now for a shake down blat before the LMC 😬 Link to comment Share on other sites More sharing options...
John Hughes Posted March 24, 2012 Share Posted March 24, 2012 I hope you'll get several blats in before the LMC *smile* Link to comment Share on other sites More sharing options...
john g Posted March 24, 2012 Author Share Posted March 24, 2012 John, how's the car show going? Link to comment Share on other sites More sharing options...
John Hughes Posted March 24, 2012 Share Posted March 24, 2012 Went today and there is plenty of stuff to look at. Well worth a trip to look round. LADS stand looked very good. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now