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Post by bodgerbedge on May 26, 2020 21:38:09 GMT 1
Hi. I have had the pleasure of restoring a 40 year old 350lc 4lO but the engine is in good condition not needing any major work. I have fully cleaned and reset the carbs including balancing and jet cleaning. The oil pump has been adjusted and she starts and ticks over nice. I can rev her but when I try to ride her then the problems begin. Firstly, she is now accelerating crisply and has a lack of power at low end. Later in the Rev range she picks up a little but now always. Sometimes I get a single PST noise and backfire. The other issue is that the left hand exhaust overheats far more than the RH one. The jets are standard and the idle mixers are wound out by 1 1/2 as suggested. I cannot hear any air leaks around the intake manifolds. Admittedly I haven’t taken the brass balls out yet for the full port clean. Timing is spot on.
any ideas? Thanks.
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Post by hoist1 on May 26, 2020 21:53:43 GMT 1
The engine has been rebuilt in the not too distant past?
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Post by shaunthe2nd on May 26, 2020 22:05:30 GMT 1
Get yr balls out! And clean behind. not sure how well you cleaned the carbs but make sure you have also removed the emulsion tubes and cleaned them as well as the main and pilot jets and other brass bits.
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Post by bodgerbedge on May 26, 2020 22:46:20 GMT 1
The engine was rebuilt a few years ago but hardly run. I rode it a few months ago and other than a lot of smoke, she ran well. I can only assume is a set up issue or something I have missed. I will try the balls removal and clean. The carbs appeared very clean and did run well before I stripped them.
I did notice when I removed the reed valves they were covered in oil and ‘sticking’ to the valve body. Was wondering if this is the case during normal running if it would restrict flow?
I still can’t explain why one exhaust Is overheating. I have removed the silencer inserts and they are not blocked.
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Post by shaunthe2nd on May 26, 2020 23:23:13 GMT 1
Modern fuel turns to a sticky glue if it's left so what you are seeing in the reeds takes place in the carbs, including sliders, floats, emulsions, air circuits etc etc hence the need for regular full strip and proper clean. It will make a big difference.
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Post by bodgerbedge on May 28, 2020 14:08:34 GMT 1
Just a quick update. I have re-cleaned the carbs and taken out the larger brass ball and found it was blocked on both carbs. do you need to also do the small ball? The ports have been cleaned out but I don't know what size that hole is meant to be. I simply pushed through with my jet cleaning file and I can't really see if there is any more crud in there. The emulsifying tube has also been cleaned. The main jet needle is set to position 3 (mid position) on both. jets are 220's which I believe are standard? I have rebuilt them, balanced then, set the mixture adjusting screw to 1 1/4 turns out, added new fuel, etc. She starts and ticks-over great but if I rev her she is very sluggish and not responding fast. Higher revs do seem better but I have not road tested her yet due to the mid range performance issue. Before the bike was stripped and cleaned she rev'd well and pulled OK. Compression is still good and by default I assume the electrics are all working OK since nothing has changed. She does appear to be very smoky and oily but I have double checked the oil pump settings and they are spot on. I can find any air leaks around the joins or intake boots. I am convinced its a carb issue but where do I go next?
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Post by shaunthe2nd on May 28, 2020 15:31:59 GMT 1
Yes its just the larger brass ball you need to remove and clean and clear the air circuit behind. You should be able to tease a thin electric wire through the hole all the way into the hollow core of the carb if its clear.
You need to put the ball back (ideally a new one) and use a bit of loctite or similar to hold it. Not too much as you don't want to clog the passage you just cleared!
220 is the recommended main jet size if your carbs are the later 4L0 01 type.
Position 3 for needle and 1.5 turns for air screw also correct.
Pilot jet should be 22.5.
Floats should be set to 21mm.
I trust you haven't mixed up the float bowls, put the choke balance pipe back on and you indicate you have balanced the carbs.
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Post by bodgerbedge on May 28, 2020 15:41:39 GMT 1
Hi. Thanks. Yes the float bowls are the correct way around. I can't see any figures on teh pilot jet but as I said, they works OK before I stripped them. I will take them off again and check everything once more.
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Post by shaunthe2nd on May 28, 2020 15:52:22 GMT 1
You could try switching the HT leads/pug caps over to feed the other spark plug. If the hot side switches with it, then more likely to be electrical. If not, then probably carburettor or air leak somewhere..
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Post by bodgerbedge on May 28, 2020 18:31:05 GMT 1
Ok. Rebuilt the carbs and no issues found. I am not sure where to check the floats 21mm setting but they seem to be working OK with no overflow. Engine still starts well and ticks over but now when I rev it, the speed goes up quickly (7 to 8000 revs) then stays there for some time before gradually coming back down to tickover. All throttle cables are loose and adjusted correctly and the slider valve moves freely. I have not seen this issue before so this is new. The rate of engine acceleration now seems faster so maybe the low / mid power issue has gone away? I am noticing that there is quite a bit of oil and smoke coming from the exhaust but the pump has been checked and seems OK. How can something so simple cause so many headaches? :-(
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Post by shaunthe2nd on May 28, 2020 20:47:27 GMT 1
Is it possible you have an air leak on one side of the head gasket?
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Post by bodgerbedge on May 29, 2020 21:48:28 GMT 1
Quick update.
checked carbs again. Reset reeds. Checked for leaks. Reset the oil pump - I set it up wrong last time. She now seems much better and freely revs. Pulls well but does have a flat spot between 4 & 6000 rpm. Both exhaust now get quite hot so I am guessing it’s running too lean? Still quite smokey on acceleration. I will check oil pump again and tweak the mixture or do I adjust the needle? It’s currently set in mid position with 220 jets. Thanks for your help.
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Post by chrisg on Jun 1, 2020 19:27:13 GMT 1
Is it possible you have an air leak on one side of the head gasket? My thought, although maybe crank seal. |
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Post by hoist1 on Jun 2, 2020 8:49:03 GMT 1
Is it possible you have an air leak on one side of the head gasket? My thought, although maybe crank seal. Is why I asked if engine had a recent rebuild. As for dropping the needles, may be worth dropping half a position, as in drop but use a shim. |
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Post by bodgerbedge on Jun 18, 2020 18:09:59 GMT 1
Hi. The saga continues. I have now refurbished the carbs with jets, etc. back to standard fitment. Checked the timing, checked for air leaks, changed the fuel and reset the reeds. The good news is that it ticks over nicely and it performs well over about 6000rpm. Issue is that it still has issues with low down revs and keeps sputtering and sometimes has a 'mini backfire'. I don't seem to see any change in rpm when I adjust the air mixture screws which makes me feel that there is an issue here. I previously took the larger brass ball out and cleaned the blocked drillings but I am now wondering if those bores are still partially blocked as I didn't know what size hole it should actually be! Does anyone have any ideas? It looks about 1mm to me.
I have also set the needle clips to mid position and up and down one as a test but I don't see any real change in performance. I am convinced this is a fuel problem as all electrics check-out Ok and there is a good spark. Any help would be greatly appreciated - I am pulling my hair out and I don't have much left! Thanks
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Post by biffa on Jun 20, 2020 16:39:21 GMT 1
Have you checked the timing?
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Post by biffa on Jun 22, 2020 0:23:45 GMT 1
Sorry, just re-read that and saw that you had.
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Post by bodgerbedge on Jul 4, 2020 22:56:20 GMT 1
Having had an enjoyable week of completely rebuilding the engine mainly to change the crank seals, today I finally fired her up. Added to this I have ultrasonically cleaned the carbs, cleaned and checked the piston and rings (all good) and renewed all seals and gaskets. Thanks to dusty’s expert advise on here it was quite easy.
So now she ticks over nice, revs a little easier and still flys at 6000rpm. Disappointing I still struggle around 4000rpm with stuttering and a lack of power.
I have put new jets, seals, etc. In the carbs, balanced them, recleaned behind the brass ball and tried adjusting the needle up and down. I am running standard exhausts with 22.5 and 220 jets. The carbs are just stamped with 4LO and it’s an early 1980 bike. Saying that it’s not matching frame and engine so I don’t know how old the engine is although it has 4LO in the cylinder casting???
I don’t have and leak testing kit so I can’t verify how tight the engine is. Timing is spot on. On the plus side the exhausts seem to be running a little cooler and there doesn’t seem to be any backfire.
Am I missing something? I still feel it’s a carb issue.
Any advise welcome.
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Post by hoist1 on Jul 5, 2020 8:49:25 GMT 1
Having had an enjoyable week of completely rebuilding the engine mainly to change the crank seals, today I finally fired her up. Added to this I have ultrasonically cleaned the carbs, cleaned and checked the piston and rings (all good) and renewed all seals and gaskets. Thanks to dusty’s expert advise on here it was quite easy. So now she ticks over nice, revs a little easier and still flys at 6000rpm. Disappointing I still struggle around 4000rpm with stuttering and a lack of power. I have put new jets, seals, etc. In the carbs, balanced them, recleaned behind the brass ball and tried adjusting the needle up and down. I am running standard exhausts with 22.5 and 220 jets. The carbs are just stamped with 4LO and it’s an early 1980 bike. Saying that it’s not matching frame and engine so I don’t know how old the engine is although it has 4LO in the cylinder casting??? I don’t have and leak testing kit so I can’t verify how tight the engine is. Timing is spot on. On the plus side the exhausts seem to be running a little cooler and there doesn’t seem to be any backfire. Am I missing something? I still feel it’s a carb issue. Any advise welcome. Just the other day was re-reading an article by Niall Mackenzie where his lc had similar issues but annoyingly it didn’t say how he solved them. His bike came with allspeeds and Keihin carbs and it carburated perfectly, he wanted it put it back to standard but then had the problem. If everything in the carbs seems correct it’s got to be worth playing with the slides and needles. Thing is, standard settings are an average like tyre pressures and individual cylinders on different bikes can have different requirements. I actually have an issue on mine, but as everything else is fine have just been riding round it. I had a dead spot at 5500 rpm during initial running in of a fully rebuilt engine, I lifted the needle a notch and now it’s hesitating just below 5000. Tempted to try carb spacers but can’t help thinking different slides and needles. |
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Post by bodgerbedge on Jul 5, 2020 9:00:40 GMT 1
What I am struggling to understand is what has changed? It obviously ran ok at some point with the standard jets, etc. Is it just a fine tuning issue or the normal performance for the RD? It seems too bad for ‘normal’.
If I have an air leak somewhere, surely I will feel performance issues through the whole Rev range?
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Post by hoist1 on Jul 5, 2020 10:16:35 GMT 1
Trouble is, it feels more than fine tuning, a lot of bikes can have flat spots in that range, though not so pronounced. Don’t think you mentioned your airbox/filter setup?
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Post by hoist1 on Jul 5, 2020 10:21:45 GMT 1
Re-reading things, Shaun highlighted the importance of the reed valves, am inclined to think they seem the most likely culprits.
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Post by bodgerbedge on Jul 5, 2020 15:58:14 GMT 1
Ok. So the air box is standard however the top half under the tank is missing and there is no filter in it - it just sucks freely straight tho’. I assume this omission is someone’s attempt to allow better performance?
The reed valves are the metal blade type with the stop leafs set to the correct opening. They seem to sit correctly on their seats when shut. They are slightly curved with some spring in them I assume this is to force them closed when not being sucked open.
I have gaskets between them plus a little smear of sealant to make sure they don’t leak air in.
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Post by hoist1 on Jul 5, 2020 19:38:39 GMT 1
You want a lid and filter really. The reed valve wants to be as flat as possible, ideally. Looking in the inside of the block with it off, shouldn’t have too much light showing, a curve don’t sound right.
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Post by shaunthe2nd on Jul 6, 2020 9:17:26 GMT 1
Running without top half of filter box and air filter will lean it off quite a bit. Suggest you fit both and the snorkel if that's been removed too and try again.
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Post by bodgerbedge on Jul 6, 2020 9:50:15 GMT 1
The snorkel is still in place but I don’t have the top section - I need to try and buy one! I can put a filter element inside as a temporary fix.
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Post by alankelly on Jul 7, 2020 22:06:08 GMT 1
Hi I thought snorkel fitted in the top lid section?  Maybe ask on here if anybody has a complete air box or just an un drilled top? Once you have posted 10 times you should get access to the for sale and wanted sections Also as a plug if you need the filter support frame bit I can supply this😏   Best wishes Al |
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Post by bodgerbedge on Jul 8, 2020 8:33:43 GMT 1
Thankyou. I have the section that connects to the carbs and runs up under the tank but it is simply missing the top sections. If I cannot get the top section in the near future I could temporarily 'fashion' something to hold the filter element but I don't know if the top section has any impact on the air intake / flow rates? I also notice a couple of holes drilled in the intake pipe. Is this a simple drainage mod?
It seems that often these filters are taken off - is it to help the engine breath easier thus increasing performance?
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Post by alankelly on Jul 8, 2020 8:44:48 GMT 1
Hi
I am no expert but yes I think the top section we’ll have a big affect on air flow (running lean and hence overheating unless the bike has been rejetted ( but you said jetting is standard?) to allow for the missing filter top, foam filter and snorkel
Also the snorkel fits inside this top section and I think this too has some affect on how the bike performs
No doubt other will be along to comment but if it was me I would ask on here if anybody has a spare top as a minimum so you can assemble as standard to get the bike closer to factory
Also on eBay at the moment there is a snorkel if needed
Best wishes Al
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Post by bodgerbedge on Jul 8, 2020 8:57:24 GMT 1
Thanks. Looks like I need the filter box plus the snorkel. When I got the bike, I was assured that it ran very well and hadn't had a filter box fitted for many years. I must admit that when I test rode it, it did feel fine so maybe something else has changed since I have rebuilt it?
On another note.... I see on eBay the 'Inlet reed cage spacer kit' adding 5mm between the cylinders and carb. Do these really help with mid range performance and will they take out teh 4k revs issue?
Thanks
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