71 cb350 twin, overheating issue?

[MOTO ARTS COLLECTIVE]

Hey everyone.. Just wanted to post this up to see if anyone had some input for me..

Little back story, I've got about 150 miles on my newly finished project. Most of these miles where fairly short rides that for the most part where pretty successful.. The other day I did an oil change,adjusted my points and valves and checked my timing chain tension.. The bike felt really good. I was ready to take it out for a nice cruise.

So heres what happened, the bulk of this ride was spent in 5th cruising between 40-60mph.. I'd say for about 20-25 miles each way. About a half mile from our destination we reach the first stop sign in a long while.. Once I come to a stop the bike shuts down.. I push it over to the shoulder put it on centerstand and kick it over.. Starts right back up but I can tell its deffinately hot.. It was smoking a bit from the head/breather vent. I would have let it sit but I was kind of in a busy area and my buddies house was right down the rd. hop back on and take it up the rd and it stalls again pulling into his driveway.. Same thing this time, some smoke but not as bad at th first time..

I'm there for a bit, it starts right up after about an hour and we go back to the center of town where I stalled the first time bout a half mile up the road. Grab a bite to eat and head home about another hour or so later..

The ride was was great.. It was dark so it was nice and cool out.. Chilly almost and the bike felt awesome. I get to the intersection about a mile from my house and the bike wants to die again coming to a stop.. This time I'm able to keep it running though and keep riding.. After that the bike started to break up under steady throttle a bitmap almost sound pingy and finally stalled again pulling into my driveway.. Again same thing little smoke and def very hot.

Here's alittle info on the bike

VM30's with stock jetting from dime city
2 into one exhaust
Mild port work to the head
Rebuilt and regasketed
Retro-fit oil cooler setup.


The bike runs really well besides this issue so it's tuff for me to point a finger at one thing that could be causing it.

My guess's are maybe my main jet is too lean?

Possible oil starvation to the head?

Dirty oil filter?

I haven't had a chance to look at the bike at all since last night but I thought maybe until I do I could bounce some ideas off you guys or see if anyone has had a similar issue.. Sorry for the long winded discription :

Here's a pic of the bike in question for the hell of it

 

[VonYinzer]

Any more info on the oil cooler?

 

[SONICJK]

71 cb350 twin, overheating issue?

Cool looking bike.
Theres a bolt on the left side of the head that doesn't seem to do anything, pull it and start the bike up and see if oil come out, if not your got no oiling at the head.

 

[Sonreir]

I'd check the oil situation and the timing again. Double-check those valves, too.

Engines are often their coolest when cruising around at top gear, so the issue doesn't immediately scream "heat problem" to me, but low oil or lack of oil to the head could be a real problem, especially if you have smoke coming from the breather.

 

[VonYinzer]

Just a thought...

Looks like your oil cooler line is tucked in on your header (at the hottest point basically). Possibly boiling the oil amd negating the effects of the cooler. Or maybe not, but as the motor heats up it starts smoking and running poorly which could be because of this.

 

[MOTO ARTS COLLECTIVE]

Here's some info on the cooler.. I drilled and tapped the primary cover right above the oil filter for a feed and return line.. Oil Is fed up the line from the centripetal force of the filter. The lines/cooler hold just under half a qt so the oil
Level has been adjusted for that. Seems like I should have enough oil in the case at all times to be ok, and you can clearly see the oil being pumped through the feed line while the motor is running.

Couple pics of the setup.

The lines are def close to the exhaust coming out of the cover but I have some really nice fiberglass/rubber insulation over the lines (not shown in the pic). Protects up to 2500 degrees so I'm hoping that would be enough to stop the oil from breaking down.. Could be a possibility though for sure..

Tell me more about this dummy screw on the head? I'm not sure I've even seen it.. I know there's def some oil getting in the head though as when I did my valves all the tappet covers had oil on them and also I have a small leak coming from my tach drive.. How much oil I'm getting though I don't know.. I'd love
To be able to pull it off and see a steady flow of oil ya know..

I'm tossing around the idea of getting some AN caps and blocking off the oil cooler to see if that solves my problem..

 

[SteveH]

I really don't see the point in the oil cooler. None of the mods you have would increase engine temps (high compression). Let us not forget that the engines are designed to have the oil at a specific temp, and cooling it below that is almost as bad as having it too hot.

 

[MOTO ARTS COLLECTIVE]

My thought was kinda based on a few different variables.. My old 550 was a really good runner.. I would notice though that when the bike was at high rpm's for a while like say on a highway ride.. I would def notice a decrease in power once off the highway due to being heat soaked.. Knowing that these little motors run warm to begin with I thought an oil cooler could definitely be beneficial...

I still haven't had a chance to get to go look at it but my plan for tomorrow is to change the oil, plugs and I've sourced some plugs for the AN fittings.. Hopefully i didn't do any damage.. :-\

On another note, what have you gents had luck with in terms of gearing? I think my next move is to try and maybe go down a tooth in the front to try to get my rpm's down a bit at cruising speed..

 

[SONICJK]

71 cb350 twin, overheating issue?

Stole this picture from the Internet
But on the top right above the cam bearing and points (electronic in this case) is the bolt I'm talking about, directly below the top right stud nut.

 

[ApriliaBill]

Did you rebuild the engine? After a couple hundred miles, it might be time to get in there and check the timing, valve clearance and change the oil to see if there is any bits in the filter. Also I don't mean to insult you, but did you check your oil lines for plugs. It could be a combination of things, the rings may have not seated, timing might be a tad off. How do the plugs look? You might have a tight lifter. Are you hearing valve float or ping? Any back fire through the exhaust or carbs? Are the valve springs correct? It could be a million things, but reality is, it could be a few little adjustments. I hope it's minor. Oh, did you sink the carbs?

Every engine is different, especially after a rebuild and it may take quite a few adjustments to meet your expectations. I don't think it's a heat issue. My experience has been timing and carbs are what is usually the issue if your valve clearance is fine, I'd head to timing and carbs.

 

[Eight40]

#1 - I race a couple CB350 engines, one is basically stock, the other is at 362cc. I don't run oil coolers. I know racers who do, but they're putting out several more HPs than mine(I'm just over 40hp). If it's stalling at idle, maybe you have a carb adjustment issue, or vacuum leak, or something else? What do your plugs look like?

#2 - Re: your gearing question: if you want less RPM at highway speed, go up in front, or go down in the back.

 

[MOTO ARTS COLLECTIVE]

Have the guys you know running coolers done anything as far as trying to improve oil pressure? Do their setups look similar to mine?

I got a chance to play a bit with the bike but haven't made much headway unfortunately.. Oil change,plugs (old plugs actually looked pretty good, left side was alittle rich but the right side was a nice chocolate color) and I replaced the leaking cam seal on the points side.. I also pulled the bolt out of the head and confirmed I'm def getting oil up there.. Pulled the petcock just to make sure it was clean.. Now the bike barely runs if at all.. Sometimes I can't even get it started.. I'm getting good spark and fuel. It's just so weird that something could have gotten so out of whack that the bike barely even starts now.. Esp because it was running so well and I didn't touch anything.

I wanted to fix the oil seal before I went any further because I had thoughts tha maybe it was fouling my points or something but that dosnt seem to be the case, next I guess I'm going to look at the valves again.. If the motor did get super hot maybe they came out of adjustment? I dunno I'm kinda taking stabs in the dark at this point.. :-\

 

[Eight40]

Have the guys you know running coolers done anything as far as trying to improve oil pressure? Do their setups look similar to mine?

I've never really looked that closely.

I got a chance to play a bit with the bike but haven't made much headway unfortunately.. Oil change,plugs (old plugs actually looked pretty good, left side was alittle rich but the right side was a nice chocolate color) and I replaced the leaking cam seal on the points side.. I also pulled the bolt out of the head and confirmed I'm def getting oil up there.. Pulled the petcock just to make sure it was clean.. Now the bike barely runs if at all.. Sometimes I can't even get it started.. I'm getting good spark and fuel. It's just so weird that something could have gotten so out of whack that the bike barely even starts now.. Esp because it was running so well and I didn't touch anything.

I wanted to fix the oil seal before I went any further because I had thoughts tha maybe it was fouling my points or something but that dosnt seem to be the case, next I guess I'm going to look at the valves again.. If the motor did get super hot maybe they came out of adjustment? I dunno I'm kinda taking stabs in the dark at this point.. :-\

I'd check valve clearance if you haven't done so since the rebuild, and then maybe compression and leak down test(assuming the spark and fuel are in fact good).

I'm not convinced it ran hot, unless you're measuring the temp, or comparing it to a similar bike?

Good luck,

Tim

 

[mydlyfkryzis]

An air cooled engine puts off a lot of heat, especially after a highway run. When you say "overheated" you really mean "Hotter than I ever seen it before" maybe?

I bet it was just "hot" within a normal range, and your perception is that it overheated.

One sure way to verify and actual overheat is that the engine will have ping and even fuel knock. When air air cooled engine actually gets to hot, the fuel ignites without the benefit of the sparkplug.

If the engine is hot, driving and moving will cool it faster than sitting on the side of the road.

Get a cheap infrared thermometer like Harbor Freight sells, and measure the head temperature. Aluminum doesn't soften till around 900 degrees, and the engine would be knocking and pinging long before it was halfway there.

 

[MOTO ARTS COLLECTIVE]

Yeah I'll def be taking a look at the valves again.. Hopefully tonight. As mentioned though they were dialed in just hours before I took this ride and the bike was running absolutely awesome.

I don't want to sound like a know it all by any means, I'm def not. I've had a number of bikes and heavily modified 2 stroke mopeds though so I know how hot these little motors can get.. I also know that I've never had one shut just down on me and pour smoke from the breather and pretty much the entire motor just was kinda radiating smoke (mainly from the head though) I have a temp gun and I think I'm going to try and fit a a temp gauge in the bolt I took out to check for oil pressure. ill have to find a fitting and a gauge that will work. First I need to get it running again though ahahahaha..

 

[Jramos13]

Im sorry to ask an unrelated question , but is that tank from a 76 cb200 or something like that?

 

[MOTO ARTS COLLECTIVE]

Im sorry to ask an unrelated question , but is that tank from a 76 cb200 or something like that?

Yessir. It's widened about 3.5 - 4 inches

Well a bit of an update.. I went back one more time and didn't have any luck getting things squared away. Everything I check seems ok. My valves are adjusted correctly, I have good compression and from what I can see the cylinder walls look to have no signs of damage/ring smear. The only thing I can think of now is maybe my timing jumped a tooth or something but I'm done trying to figure it out.. I loaded it up tonight and am dropping it off at a very highly recommended vintage Japanese bike shop in the morning.. Hopefully ill have some good news towards the end of this week and will be riding again shortly after.. Wish me luck gents!

 

[MOTO ARTS COLLECTIVE]

Well still battling with this thing.. Bike was at a shop for a week, was called and told it was all set so I got a ride to go pick it up. On the ride home it ran like complete shit.. Spitting, cutting out and finally shutting down and overheating on the side of the road... Once it was cooled down I started it back up and took a video to share and see what you guys thought.. Don't mind the stuff before its running, the vid is also for a potential buyer so I just wanted to show everything working for him...

http://i230.photobucket.com/albums/ee204/dubsbro1/DF87A0C4-4E78-4552-8D78-6F3005669166-22830-00001DF94A3CE823.mp4

 

[mydlyfkryzis]

Exactly how do you know it overheating? Have you taken a reading with an infrared thermometer or anything?

Sounds more like vapor lock, the gas boiling in the carb, or something on that order.

I've heard a lot of people claim their bike was overheating, but I am not sure of they are correct on this. I used to ride my CB350 "off road", high throttle, slow speeds. It got HOT, it ticked and smelled hot, but continued to run fine.

An aircooled engine can run over 200 degrees "normally", which from a "hand near the cylinder head" reading is quite hot. But unless it is seized, or knocking from pre-ignition, I doubt if the engine is actually overheated.

I've idled in traffic on a 101 degree day, and the engine was very hot, the heat was baking my legs, but it was not overheated, just HOT.

I am not trying to be snarky, but you may be looking for the wrong problem.

Look at the plugs. An overheated engine will damage the plugs....they will have little balls of metal on them...When overheating, the aluminum softens, and vaporized aluminum will collect on the plug electrodes.

Or buy a less than $30 infrared thermometer from Harbor Freight. then you have an actual temperature.

Edit: I reread the post, I see you have a thermometer...do you have a number? That would be a better judge of the temperature.

Also, check left and right...maybe one cylinder is hotter than the other, carb sync, carb fuel feed, etc....

 

[joea]

so much for the great shop.........you need someone that knows how to time and jet your engine. if it was really overheating and seizing it would be apparent visually when you looked and also when you did the compression test... those tiny air filters are not very good either in my opinion. if your engine was warmed up in your video it's lean off idle.
joe@vcycle
www.joesvcycle.wordpress.com