Got the oil changed, and took it out to give it the beans.......

[Guest]

....and it's got a bit of a bog. Free revving in neutral, it will only rev to 5 or 6k. I'm not familiar with how these engines feel when running perfectly, but it feels pretty smooth up to the point that it bogs, and it sounds healthy enough.
In gear and moving, it will also bog at anything above half-throttle. If I walk it up slowly, it will go past 6k rpm, but will bog if I try to pin it. But again, it will pull smoothly under half-throttle.
No smoke or anything, and no rich smell to the exhaust. I'm unsure of the jetting in the carbs, but I talked to the previous owner, and he said he never touched them other than to get them rebuilt (which is where I took possession of the bike). I prefer to not tear these freshly rebuilt carbs apart just yet, so I want to try everything else first.

I do believe the air filter is probably pretty dirty, and I'm not sure how sensitive these engines are to dirty air filters. I also noticed it would only stay running with the petcock set on prime. I did discover the vacuum line was kinked, so could that have had something to do with either issue, or even both? I replaced the vacuum line with something a little firmer, and did not find any kinks. I ran out of light, so I'll mess with it again tomorrow.

[cowboyup3371]

Don't trust the po that those carbs were rebuilt; mine said the same thing but a closer inspection of one badly varnished bowl quickly proved he was lying. Ed (Nessism) says it best - to measure is to know. Take the time to measure and know your bike's current condition or you will be fighting it for a long time

[BassCliff]

Hi,

Unless you cleaned and rebuilt the carbs yourself you do not know that they were done properly. The usual suspect in a "bogging" situation is an air leak. Have you gone through the maintenance lists in your "mega-welcome" and properly addressed all of the know issues with a 30 year old motorcycle?


Thank you for your indulgence,

BassCliff

[Mr. Sinister]

Well, I saw them get rebuilt, so I know they were. A good friend of mine, also a biker, works at the shop that did them. My The guy who did them has a pretty good reputation, as well. But, nobody is perfect.
It idles perfect, it runs under partial throttle well, it just bogs when I try to open it up.

I am going through "the list" as I go with this bike. I replaced the carb to head boots and made sure the o-rings were good. I rebuilt my petcock, and checked its operation by applying a little suction to the vacuum line, and felt the diaphragm pop back and forth, the carb to airbox boots checked out ok, and the exhaust is in excellent condition. I have yet to check the valves, and the seal around the air filter and airbox, and clean/replace the filter

[exdirtbiker]

"I replaced the carb to head boots and made sure the o-rings were good."

please...please replace those o-rings the next time you have the carbs off the bike.
they are cheap.
they are 33 years old????? Yikes !!!! Change them, it's one less thing you will have to worry about for the next 10 years!

[Mr. Sinister]

Well, I got a set of boots from a friend of a friend that was parting his 450 out, and the o-rings on those boots checked out. Still round (not flattened) and no cracks. I'll replace them anyway at some point.

[tkent02]

I'm not familiar with how these engines feel when running perfectly, but it feels pretty smooth up to the point that it bogs, and it sounds healthy enough.

It should accelerate smoothly up until 6,000 or so, then take off like a shot.

Clean the carburetors. Adjust the valves. Do it all.

[Mr. Sinister]

It should accelerate smoothly up until 6,000 or so, then take off like a shot.

Clean the carburetors. Adjust the valves. Do it all.

I felt a bit of that, actually.

Oy. Looks like I have a busy weekend ahead of me.

[BassCliff]

Hi,

I have a friend with a 450 and his airbox has been notoriously leaky. He had issues with surging and a 6000 rpm "ceiling" until he finally took my advice and completely went through the air intake system. He replaced the airbox-to-carb boots as well as the intake boots and O-rings, sealed the airbox with weatherstripping, raised the needles a bit, and now it runs like it should.

Adjusting the valves helps it breathe better too.

Thank you for your indulgence,

BassCliff

[Mr. Sinister]

Well as it turns out, there is NO air filter, just an empty box with what looks like 2 layers of wire mesh towards the front. There is also no lid for the box. Time to start looking for the parts, I guess.
I did find the airbox to carb boot clamps loose enough to spin, so I cinched them down.

And I guess I need a new petcock. Bike won't run and pops through the exhaust unless it's on prime.

[BassCliff]

Hi,

Yep, it sounds like you're getting too much air in the air/fuel mixture. Any modifications to the intake or exhaust usually require jetting changes to keep the air/fuel mixture in balance.


Thank you for your indulgence,

BassCliff

[Mr. Sinister]

I would assume that's the case as well. I think the airbox to carb boots are leaking, even after tightening them. I swear I can feel air moving if I put my hand by them. When I had everything apart, I pulled the box away from the carbs. I put it back together and went for a spin. Whatever I did made the bog worse, as it won't rev about 4500 or so in gear now. So I think I'm on the right track.
So I'll be changing those boots, and I figure I might as well put some new O-rings in the carb to head boots while I'm at it. I'll be sure to seal the filter when I get it. If I can't find the airbox lid, can I cover the opening partially with (apologies) duct tape to restrict the airflow a bit?
Tagging the thing today cleaned me out, so maybe next paycheck.
Good news is changing my fork oil and setting the rear shocks to their firmest setting made a WORLD of difference.

[pete]

If it won't rev like that, you might also want to verify that your advance mechanism is actually advancing... If it doesn't rotate freely and spring back then that will impact the ability for the engine to increase rev's.

Aside from that, duct tape to restrict airflow will definitely help and is fine for a temporary test setup, but just make sure it's taped firmly and use long bits so it doesn't get sucked into the carbs

[1_v8_merc]

Do you have an Inline fuel filter installed? If so, remove it. They can create walls.

Also, the Float Height can be set wrong. If it's set too low, you'll be extremely lean, creating a Wall.

If it's not either of those, it has to be a vacuum leak.

[Mr. Sinister]

OK, so I got to thinking, what can I do to restrict airflow a bit until I can get the right parts. So I dug up the foam I used for my seat pad, and made a makeshift filter. I cut a piece to go against the wire mesh at the front of the box, and 2 pieces to wedge in behind it along the edges to keep everything in place. Everything fits snugly inside the airbox. I then used some duct tape to create a V shaped opening on the top of the box. While I had it apart, I checked my airbox to carb boots, and found the right side boot was rolled under, and not sealing. Fixed that, and put everything back together.

Crazy enough, this seems to have solved my bogging issue. It revs freely in neutral, and doesn't smell overly rich (maybe just a hair fat, but not too bad). I took the bike out for a good ride, and spun it up to about 10k and had it up to 60mph. It pulls up nice and smooth, and has decent throttle response for what it is. It's certainly no speed demon (especially with my 240 pound frame on it), but I was pretty impressed by how well it pulls up. Once I get more familiar with it, and check the valves, I'll do a few redline pulls and see how it feels.

Thanks to everyone for their input and advice, I greatly appreciate it!!