Honda CBR1100 Carbs

The Despair Shop Part 8 – It’s All About Balance

Despair shop part 8 – It’s all about balance.

The CBR1100 Super Blackbird went to it’s new home, which was the same home as the SV650 – very convenient. Bloke came with his girlfriend to see the SV and bought that and the CBR as long as I got an MoT on it. I knew it would pass, it only had one advisory cos Julian felt I had done the chain up a bit tight. He was right so I slackened it off a tad and delivered it to it’s new owner.

I can’t remember the last time the workshop was this empty, all it has in it at the moment is the RS125, my part built cafe racer and as from today the CBR1000F that I have never quite got to.

I knew it had a really bad misfire and a significant rattle at the top end, which I have always assumed to be cam chain rattle due to a knackered tensioner – they do tend to suffer from it.

So I whipped the cam cover off to have a look and now I don’t think it is the tensioner. Having seen nothing obvious I put it back together and had another listen with a stethoscope, I’m pretty certain it’s a loose tappet. I ran out of day and energy so I will have a look tomorrow.

While I was at it I thought I would check out the misfire – my infra red thermometer showed me the exhausts for 1 and 2 were running at about 160 degrees – 3 and 4 were at about 30. Honda CBR1100 Thermometer

Here’s my digital thermometer in action, this photo was taken after I sorted out 3 and 4 but before it was fully warm. They seem to run at about 250 degrees when everything is hunky dory. It does depend where you measure them though – always try to measure at about the same distance from the head otherwise the readings can be a fair bit out.

I popped the plugs out – they were dry but really black, neither were sparking with any degree of enthusiasm. A new set went in but 3 and 4 were still being grumpy so it was off with the carbs for a good old look over on the bench.

Both idle jets were well and truly blocked and there was some grot in the bowl of carb 4. Getting them back on was made a lot easier by the judicious application of some tyre soap – the stuff they use at PrickFit when they balls up putting your tyres on. That’s a story for another day though. Anyway, I filled the carb bowls using my trusty old outboard priming bulb and the engine runs way better now. It’s still not perfect as I think the carbs are a bit out of balance, I’ll go through them tomorrow and see if I can get it better, it will then be back off with the cam cover to check the tappets, particularly on 1 and 2 inlet.

Adjusting the carbs on these is a proper cow as the screws are in a really awkward position. It’s unusual for a Honda which are normally so well thought out. I reckon the usual bloke had a week off and they got some sociopath in to fuck with people’s heads when they designed this one. Matters are not helped by the fact one of the vacuum take offs has been replaced with a blanking bolt, probably because the brass take offs are very easily broken and some clumsy sod has been there before me. I might make a new one as it’s an excuse to play with my lathe for a change or I might just swap them around and set the carbs in pairs as per my previous exploits when I only had 3 gauges available.

The thermometer suggests that number 4 is doing less than the other 3 as the downpipe is about 30 degrees cooler than the other 3 so they definitely need setting.

Oh before I forget, I got the new points for the little Italian beast I talked about in the last episode, looks like my hunch was wrong. The points don’t fit so I have to assume the ignition stator plate is the Dansi one after all and that the flywheel is the wrong one – it’s a 3 hole Bosch, I need the 2 hole Dansi one – God alone knows where I am going to get one from. It might take a while but I’m sure one will turn up one day.

Honda CBR1100 Cylinder HeadBut for now – back to the CBR1000F and a damn fine lesson in not assuming things. I had assumed it was the cam chain tensioner causing the bad rattle but on reassembling and having  a proper listen with a stethoscope it sounded much more like a tappet rattle on number 2 inlet so I took the cam cover back off for a better look. It didn’t take long to confirm what I heard – the lock nut on one of the inlet rockers was completely missing! I had been so sure it was the usual cam chain tensioner that I simply hadn’t looked properly at what else it might have been. I now have to wait until a 7mm fine threaded nut turns up before I can go any further on this one. I also have to find out what happened to the missing nut. I guess dropping the sump is my only option – I hate bikes sometimes.

I’ll let you know how it goes next time – bye for now, Dave.


Article provided by David Powell of Boston Bike Bits.

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