Carb experts wanted!

[mcgovern61]

RBG, watch this video and listen to the knock at .48 seconds of the video and further. The video is a cold start of the engine up right on center and after startup I lean the bike over to the side stand and the oil pressure drops off. As the engine begins to warm, the pressure stays low but recovers slightly when the bike is upright again. I am raising the throttle speed using the choke cable:

https://www.youtube.com/watch?v=SPysWst04xk

[video]https://www.youtube.com/watch?v=SPysWst04xk[/video]


It is that knock that increases in volume while riding.

 

[dan filipi]

I notice right at .46 seconds you pulled the chock on full. Then the knock came on hard and the engine speed dropped.
Could that be related?

 

[mcgovern61]

The engine speed dropped because I was pushing in the cable ever so slightly to that sweet spot that would make the engine knock. I was trying to see if it was a specific oil pressure that made it knock, but it was not consistent.

 

[mcgovern61]

WOW just a major thought at least I think it's major..IF your gas cap was partially plugged it could starve you carbs and make the engine run like crap at high RPM's..as you described..cylinders cutting out due to gas storage would mark the engine run like it was out of synch at high speed..and could sound like a diesel..knocking as it would be out of balance????? worth a check before you swap out an engine with 160 compression numbers!!!!

Or this could be a brain fart???? what do you think Dan???

When I accelerate quickly, the engine detonates (or sound like it) although the spark plugs do not show signs of actual dieseling or detonation. I had the carbs rebuilt with the Randakk kit and a professional. When they came back, I could idle down to 650 and still run and the power was a little better, but I still got that hesitation and loud banging when I jump on the throttle while already at speed.

Vacumm in the system could very well be one of my problems!

 

[mcgovern61]

RBG, before you start think oil flow could be a cause of the knocking, watch this:

https://www.youtube.com/watch?v=ZPKca7Oiwjs

[video]https://www.youtube.com/watch?v=ZPKca7Oiwjs[/video]

And that is only at idle!

 

[fastmover83]

That doesn't sound like a knock, to me, it sounds more like a harmonic rattle, possibly from the bolt that holds the alternator stator in place. They can have a habit of backing out, especially if the bike has had alternator work in the past.

 

[mcgovern61]

That doesn't sound like a knock, to me, it sounds more like a harmonic rattle, possibly from the bolt that holds the alternator stator in place. They can have a habit of backing out, especially if the bike has had alternator work in the past.

I thought the same, but the bolt is tight. The sound comes from the center of the block just behind the heads on both sides.

I have to admit, it is a strong design, I have put over 8,000 local miles on this engine even with all of its noise and it still is going (except for the fact that there is no gas in it right now as I diagnose the carb problem).

 

[thewhiterhino]

Another thing to consider is the fuel pump. :read: If the diaphram is leaking the fuel that bypasses can end up in the oil. If it is leaking it will quit completely one day of it hasn't ruined an otherwise good engine. :shock: :shock: :shock: That is a plus of having a dipstick and checking the oil regularly cause you will see the increase and smell the gasoline. :razz:

 

[mcgovern61]

Well, I started testing today. Pulled the seat, shelter, faring, filter housing and gas filter. Refilled the gas tank and topped it off. (Added some seafoam for stabilizer, it is only 28 degrees here.) Removed the gas filter and opened the petcock to the reserve position first - no gas. Moved it to the open tank position - no gas. Cracked open the gas cap with the petcock in open tank position and gas flowed freely! Closed the petcock with the cap open - gas stopped flowing. Conclusion: petcock is working, gas cap not venting. The gas cap is rusty underneath.

The fuel filter was pretty clean, but changed it anyway.

Dropped the oil (which really took a long time with these temps) and refilled with fresh oil. Battery is fighting with me so continued to keep charger on it while cranking with the plugs out. No gas in the cylinders. Start the bike (after much cranking to refill the carbs) and run it up to temp for 1 hour. (Ahh, heat! :yahoo: )
No sign of gas in the bottom of the plenum yet. Now I am letting it sit overnight with the petcock closed and the plenum open to see what happens.

 

[RBG]

I guess I missed the metal bits..noted the sand..where could have that come from?

 

[joedrum]

thats a shame about the sand and metal. either fix the cap or run it without cap to hyway speed i think rgb has a point on the vacuum. it can't be totaly trashed motor running 6000 rpm at 70mph. sounds like love in reverse gear on the sand in the motor ouch. if it was me and i had another motor i'd go that way. this gearing difference is not a good mix in my opinion unless you want a street rocket. an 82 or 83 bike can take a 1000 motor and end up with about 3400rpm at 70mph making a nice touring bike but the 80 81 motor with all the issues i would get away from.

 

[tumunga]

I couldn't begin to tell you what that noise is, but I can, with confindence, say that isnt' a rod knocking. I know you said the noise is coming from behind the heads on both sides of the engine, but have you tried one of those mechanic stethoscopes to try to pinpoint the location of the sound?

 

[mcgovern61]

I guess I missed the metal bits..noted the sand..where could have that come from?

The PO was a college kid and he tried to make an '81 Interstate into a race bike by stripping it down naked. I have the feeling some one at school may not have been friendly with him! :shock:

The only way I can figure sand shows up in the oil pan and in the filter is some one has to pour it in! (This is one tough engine!!)

Unfortunately, there is visible metal in the oil at each oil change, kinda sparklely, but it still keeps going! (Did I mention that this is one tough engine!)

 

[mcgovern61]

I couldn't begin to tell you what that noise is, but I can, with confindence, say that isnt' a rod knocking. I know you said the noise is coming from behind the heads on both sides of the engine, but have you tried one of those mechanic stethoscopes to try to pinpoint the location of the sound?

Eric, I did take a stethoscope to the engine, but there is so much other noise it is very difficult to pin it down, particularly when the engine has to be up around 3000 RPM to find it. Besides, in my head, I cannot picture which mechanical part can be tapping together to make that noise (other than valves or stuck lifters which I did check and they are ok). When it starts, you can hear that the innards are loose and knocking until the oil pressure comes up.

 

[mcgovern61]

thats a shame about the sand and metal. either fix the cap or run it without cap to hyway speed i think rgb has a point on the vacuum. it can't be totaly trashed motor running 6000 rpm at 70mph. sounds like love in reverse gear on the sand in the motor ouch. if it was me and i had another motor i'd go that way. this gearing difference is not a good mix in my opinion unless you want a street rocket. an 82 or 83 bike can take a 1000 motor and end up with about 3400rpm at 70mph making a nice touring bike but the 80 81 motor with all the issues i would get away from.

You are right, it is not a totally trashed motor because it starts every time, does not blow smoke, is 160s on the compression and does have some ponies! I think the bearings may have taken a hit from the sand which more than likely mixed with the oil and ground into pumice. (Although they were about 80 grit size particles that came out of the filter).

I have the '83 swap engine just about ready to go in if I can find the time. My best mechanic/helper (my 18 year old daughter) is at college in Florida and I might actually have to do the work myself. (She swapped the blown '82 engine with the'81 with me)

 

[joedrum]

wow thats neat your daughter puts in time and intrest on your wing. im sure the loss of help going to take a lot of fun and enjoyment out of the project.

 

[mcgovern61]

wow thats neat your daughter puts in time and intrest on your wing. im sure the loss of help going to take a lot of fun and enjoyment out of the project.

It is a loss, she never worked on anything mechanical before, but she has a lot of common sense. When we first got the bike I was only letting her remove the seat and stuff. Well, I needed more help so I told her to take off the bags, faring and seat and when I came back out 20 minutes later they were off. ONWARD and UPWARD! I told her to take out the carbs and cables and she said, " I have never done that before?" I said, "A person assembled all of this, a person can take it apart. Find tools that fit and get started!" I found out that if Dad says "I can do it" she does it without question. Within two weeks she had the old '82 engine out and on the floor and the bike down to just a frame! (Of course I wasn't worried about damaging the '82 engine, it was blown.) :smilie_happy:

She worked with me stripping, sanding, painting, swapping and she put the '81 engine in. (BTW she was 16 years old then!)

Yep, I miss my work partner cause now I have to get my own hands dirty! :cheeky:

 

[mcgovern61]

Well it has been 3 days of sitting in the cold garage and no signs of leaking. :clapping:
I did drain out the carbs by running the engine last month and maybe sitting without gas in them let the floats and needles go dry. Maybe that is all that was needed? I am going to let it sit some more and prep for another snow storm.

 

[vulkan 95]

I had my carbs rebuilt last spring and they came back working like a champ! Rode all summer til Fall without any problems (Except for that fact that the engine sounds like a diesel, but that is another story. I have a transplant engine going in soon, I hope.)

Last December as the bike was sitting for about 3 weeks, it decided to leak out the gas from the carbs into the intake manifold.

Not being a carb expert, is there something simple I should do to find the leak? I am assuming float needles and all that stuff, but have never worked on carbs. (Well, maybe once on my parents old '69 Ford LTD wagon, 390 engine. Ended up with a Cardo carb kit if you guys have ever delt with them.) :help:

Any help is appreciated! (Funny things is, I do not mind tearing down an engine to it's last bearing, but carbs have always scared me!) :nea: :smilie_happy:

Ethonal, man eats the rubber right out of some of the old carbs, Disolved 175 bucks worth of diaphrams in my Vulcan, replaced the float bowl gaskets in the Interstate and shut of the fuel and run the carbs dry. Can't be helped since we are forced to burn the combustable water downed crud.

 

[vulkan 95]

RBG, before you start think oil flow could be a cause of the knocking, watch this:


And that is only at idle!

Sure it's not in the clutch, flywheel, throwout bearing area? Does the noise change under load? Clutch engaged or dis-engaged? Just full of questions aren't I? I have heard rear mains chatter kind of like this too. Might be a jack shaft bearing, but not likely if the machine has never ran low on lubricent.