Hi All,

Just finished building my '97 CBR and went to take it out on her maiden voyage the other week. When I was out on the road, there was no power what so ever from the engine, it even stalled once or twice when I was turning into a junction. The bike will respond beautifully to the throttle when it's on the paddock stand, but as soon as you put any load on the rear wheel... it goes!

I still think that the carbs havn't been balanced correctly and that is why it seems like it;s not firing on all 4 and appears to be choking out.

Was just wondering if any of you mechanical geniuses could shed any light on the problem and help with a solution?

I understand there could be 101 places to start so I'll give you a brief run down on the situation...

• New spark plugs
• New oil & filter
• Fresh water
• Carbs have been cleaned in an ultrasound tank
• tank has been cleanded out
• Carbs have been balanced
• camchain replaced

Thanks very much!

 

Do you have all the vacuum hoses attached to their proper location ? Having no power under load sounds like an issue with a vacuum leak. Take the tops off the carburetors, the black lid with 3 screws and make sure that the diaphragm is properly seated in the groove. Also, do you have the speedometer connected ? There is a solenoid that is activated at 12 mph, so the speedometer needs to be connected. These are just some ideas.

BTW, it's an "Ultrasonic" tank. An Ultrasound is something that pregnant women have done to check on their baby... LOL, sorry couldn't resist.

 

Thanks IDoDirt, I will check these at the weekend.

It's an aftermarket Koso speedo, but it's been wired in by an auto electrictian - so I hope it's been done properly! Lol, but will check this too.

Haha I was meant to type Ultrasonic! Thanks for pointing it out though 😆

 

IDoDirt,

Checked all the pipes and their all connected properly. Literally just come in from taking the bike out again, the power issue is more mid range, but when you hold open the throttle.. it clears through! Buttttt then when you change up a gear, you then go back to square one where the power dies away!

I've seen another one of your posts about the fuel filter connections, so I've ordered an aftermarket one and when it arrives I'll be popping this on the bike to see if that eliminates the issue.

I don't think it is a solenoid issue, you can get over 12mph no problem.

Thanks again!

 

hi townsend,

did you ever get to the bottom of this?

if you change the gauges the air solenoid needs to be addressed. you're auto electrician isn't likely to have known this. its also known to be a problem only when under load.

sounds like air solenoid valve is stuck in its 'under 12mph mode' to me. if you have an aftermarket gauge it can get complicated dependant on where you're taking the speed signal from. if thats the case you can either ground the valve to think its permanently in its secondary vacuum mode or you can remove the valve completely. theres a couple of write ups on it here on the forum.

i went through a fair bit of fuss to try retain both stages of ram air when changing gauges and in the end hauled the valve out and rerouted the hoses. played with the idea of generating the right current to activate the solenoid valve but it is way more hassle than it will ever be worth. they say you're as well off doing away with the 1st stage of ram air if you even have an aftermarket can as the tolerances for its vacuum is incredibly specific, even more so if you're using high flow air filters or jetting changes.

it runs just as well without the valve.

definitely something worth looking at first but the other symptoms do sound like a vacuum leak for sure. hard to tell without seeing it. hope you get to the bottom of it.