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Post by looey on May 13, 2013 21:27:59 GMT 1
Ok, so after stripping the top end on my YPVS engine to find most of it beyond its sell by date, I took the plunge and purchased a compete top end with all new TSS valves that had been removed from a known good runner. I've now fitted the new top end (pistons, barrels with valves and head) but now it runs very badly. Everything else is identical, i.e. just swapped reed assemblies and carbs etc. from old to new. It starts easy and runs ok (ish) and if you pootle about on very light throttle inputs under 5,000rpm you wouldn't suspect anything is wrong, but give it any amount of throttle or try and make it pull through the mid-range and it just stutters, misses, farts and backfires going nowhere fast  . I was aware the new barrels were tuned (unkown though) but my old barrels are Mick Abbey tuned and it's running Vforce3 reeds and PWK28's and ran pretty well so wasn't expecting much of a change. Don't have any other pics cos it's all fitted now but just looking at the inlet tracks and ports (see pics below), the new barrels have massive openings compared to the old, so just wondering if anyone thinks this could be causing me the problems with my reed/carb setup ?. If all else fails I'll get the original barrels sorted and re-fitted but I'm hoping this is a silly problem I can fix without rebuilding the top end AGAIN...... lol   |
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Post by 47x on May 13, 2013 21:30:44 GMT 1
they look home made to me chap,or unfinished??but i could be wrong...is there ANY engraving on them??
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Post by midlifecrisisrd on May 13, 2013 21:40:20 GMT 1
I hope they are not a pair.
Bottom one looks massively tuned and top looks like a diy job.
No wonder it runs like a pig
Steve
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Post by 47x on May 13, 2013 21:41:30 GMT 1
thats not as far as i would have gone...but fair play to you steve,its true m8!!
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Post by looey on May 13, 2013 21:43:09 GMT 1
I hope they are not a pair. Bottom one looks massively tuned and top looks like a diy job. No wonder it runs like a pig Steve No they are not a pair....lol. The top picture is ONE of my old barrels which it ran nicely on.... the bottom picture is ONE of the new which it runs like a sack of sh*t on....  ;D Each pair are matched (as far as the eye can see) |
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Post by midlifecrisisrd on May 13, 2013 21:53:08 GMT 1
That makes things a lot better lol Top one looks like a mild tune where as bottom one is a bit wilder so carbs may be way out. Don't look too bad though, here's my abbey ones  Steve |
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Post by looey on May 13, 2013 22:01:24 GMT 1
Yeah my new ones don't look that different to your Micks Abbey ones there.
It's easy to make them look quite a bit different just with camera angle but they are similar.
Mine has PWK28's running 145 mains, could the tuning be that different that it would run that badly, almost like it has an ignition fault stopping it revving ?.
It won't even rev up in neutral !. Give it a load of throttle and it just missed and farts and sounds awful.
Basically I need to determine if something's happened during the rebuild to upset something that was ok before or if these barrels are totally incompatible with my old setup that it won't run at all ?.
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Post by midlifecrisisrd on May 13, 2013 22:06:01 GMT 1
They do not look much different but mine is stroked so not sure if the height of yours affects it badly.
Does sound a bit severe it wont rev in neutral. Like something else is wrong.
I'm lean on 135's so looking at 140's so your carbs can't be causing that much grief.
Steve
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Post by Deleted on May 13, 2013 22:08:44 GMT 1
Did you have the pwk s on before? For my 4lo had to go down on the mains and up on the pilots when I put pwk carbs on
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Post by looey on May 13, 2013 22:12:03 GMT 1
Did you have the pwk s on before? For my 4lo had to go down on the mains and up on the pilots when I put pwk carbs on Yep, I've only changed the pistons, barrels (with new valves) and head. Absolutely everything else is identical and just swapped from the old to the new, even the temp sender !. It ran pretty nice before but was spitting cr*p all over my boots from the valve seals |
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Post by Deleted on May 13, 2013 22:16:33 GMT 1
Know it's a pain but could you put the new valves in the old barrels
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Post by looey on May 13, 2013 22:30:24 GMT 1
Yeah that's what I said at the end of my first post I will do if I can't get it sorted but one of the barrels is cracked and needs welding, and the bushes have been moving so a sloppy fit now (I'm told you can fit them in-place with silicone) . Not going well this ;D ;D |
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Post by Deleted on May 13, 2013 22:37:12 GMT 1
Bad luck looey sure you will get through it
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Post by nikfubar on May 13, 2013 22:42:29 GMT 1
Yeah that bottom pic looks like a race tune  more opened up than my fast road tune from Mick. Wouldn't have thought it was anything to do with the carb jetting, 145 mains are lean if your running pod filters (most run 152s) & would make it very zingy & rev out quickly. Maybe it's a plug or loose connection breaking down under load  |
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Post by looey on May 14, 2013 7:22:12 GMT 1
Maybe it's a plug or loose connection breaking down under load That's what I'm hoping/praying for but strange it appears out of the blue at exactly the same time as the top end is swapped out but I suppose something could've been disturbed (a bit like I am lol) I suppose. It's not the spark plugs, as I've changed both |
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Post by looey on May 14, 2013 8:38:38 GMT 1
The seller said they came from a bike that he rode for a few days to make sure all was well in the engine and said it ran "spot on" with 31k carbs and std airbox, so I have to assume for now that something else is wrong or has gone wrong swapping the top ends over. It'll be just me luck that something totally unrelated has gone ratsh*t and will take me lifetime to find/fix If I get to the point of re-fitting the original top end (once it's all been repaired), then I'll probably send them to Mick to see if he thinks there's any reason he can see why it wouldn't run ok. Nightmare....lol |
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Post by jessy03 on May 14, 2013 17:48:32 GMT 1
Look similar to a set of barrels I have, they worked well on my 31k, Pwk, modified air box and early kenny pipes. I would double check your electrics, something may be loose. Jess  |
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Post by bare on May 16, 2013 2:37:53 GMT 1
Those intake ports were "fooled' with but Hardly tuned OR expertly done.
Having said that those make Little to Fook All real world difference.
Why? are your Mains problematic? I run 130's 40 air jets and it works V Well :-)
Also decently ported by a Seriously Good tuner, West Coast of USA though ...Not UK :-)
What is the rest of the intake tract?
I run oem Airbox and a 'slightly' freer flowing filter material element though
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;D
more opened up than my fast road tune from Mick.
